Move SFTP and S3 into the tab strip, and the host list into a card grid

Four asks in one pass over the desktop head, and two of them are furniture
moving rather than anything new.

THE STRIP IS THE WINDOW'S NOW, not the terminal's. Vaults, SFTP and S3 sit at
its head and cannot be closed, and open terminals follow them. SFTP and S3 left
the nav rail to get there, which is the one semantic change: they are the two
destinations you stay in while something runs, and a rail entry is for
somewhere you go and come back from. So the rail belongs to the Vaults tab and
collapses with it, which also means SFTP, S3 and a terminal each get the full
1016 rather than the 826 a page gets.

The tab is expressed as "a page, and not one of the two the strip took" rather
than as a fourth ShellSurface. Both are still ShellScreen members and have to
be — that is what they are on the phone, where they are two rows in a hub — so
a surface each would have been a second way to say a thing Screen already says.
IsTransfersShowing and IsBucketsShowing light the other two tabs unchanged.
What is new is one field: the page Vaults comes back to, because it is the one
tab with sub-navigation and therefore the one that can return to the wrong
place. That is not the hidden field ShellSurface argues against — that one
would be a second copy of "which page"; this is a tab remembering its own.

THE HOSTS SCREEN IS A GRID, and the 268-pixel sidebar is gone. That column was
choosing among forty machines and editing one of them at two-thirds width, and
it was narrow so the editor beneath it could be a column at all. Cards took the
first job at full width; a 304-pixel drawer took the second and collapses when
nothing is selected. Pressing a group card narrows the grid; SHOW ALL is the
way back. The group editor moved into the drawer as well, which finally makes
IsEditingGroup mean the same thing on both heads — it was the phone's alone,
because the desktop's editor was a bar that was always on screen.

AreHostsExpanded and ToggleHosts went with the control that used them. They
folded the whole list away under one heading, an affordance that existed
because the column was narrow. Folding a single group is a different thing and
is still here.

THE TYPE SCALE IS A POINT LARGER and the text ramp is white. The base size was
never stated anywhere — a bare TextBlock took TextElement's default of 12 — so
raising the scale meant naming it, on Window and on UserControl. The second
selector is not redundancy: the layout harness hosts a UserControl in a window
it builds itself, and without it the suite would measure every screen a point
smaller than it ships, silently. A selector on TextBlock would have been the
obvious way and is wrong, because a style setter beats an inherited value and
would collapse every deliberate step back to one number.

#E3E7F4 is a blue-tinted white on blue-black surfaces, which costs contrast
twice — once for being darker than white and once for sharing a hue with what
it is drawn on. Pure white is 18.3:1 against the canvas where that was 15.5:1.
Every step below moved with the top, so the intervals the design chose are
kept and TextDim clears 9:1 against 6.4:1. The palette is shared, so the phone
has both changes too.

TWO DEFECTS THE HARNESS STRUCTURALLY CANNOT SEE, found by rendering the screen
rather than by measuring it, and both now covered.

The tile was 232 and was first written as 248, from arithmetic that left out
the scrolling stack's own margins. Every layout test passed — the harness asks
whether a control is inside the window, never how many fit on a line — so the
grid quietly became one column wide at exactly the minimum this application
guarantees, which is the shape cards exist to avoid.
TheHostsGridKeepsTwoColumnsAtTheMinimumWithTheDrawerOpen counts columns
instead, and fails at 248.

And a card's text ran past its own border, because a horizontal StackPanel
measures children with infinite width: a TextBlock inside one never learns it
is short of room, so TextTrimming never fires. Both card rows are grids with a
star column that gives way and an Auto column that does not — a hostname with
its tail cut is still the machine you were looking for, where a badge or the
word naming an auth method is not.

The keychain header changed shape for the same class of reason. It was
Auto,Auto,*,Auto with the buttons last, so the slack column was the only thing
absorbing a change of width and five buttons fell off the right edge the moment
the type grew. That is how GENERATE lost the word KEY once already. The summary
sits in the star column and trims now, so the buttons always get their width.

HostSidebarTests became HostGridTests and moved to the grid with the gestures
it drives. docs/design-import-gaps.md gains a v3 section naming the five
toolbar controls in the design with nothing behind them — a view-mode switch, a
tag filter, a calendar, a share control and Serial — and manual-checks.md and
the README follow the controls that moved.

README.md

@@ -148,8 +148,9 @@ dotnet run --project src/DodoSSH.Client.App
 In the app, enter `http://localhost:5233` as the server. Your browser opens for sign-in — the realm ships
 `alice` / `alice` — then choose a vault passphrase and **write down the recovery code**, which cannot be
 skipped and cannot be recovered from the server. You can then add a host and open a shell on it — double-click
-it in the sidebar, or select it and press **CONNECT**, which is the same command with the password box beside
-it. Keycloak's admin console is at `http://localhost:18080` (`admin` / `admin`).
+its card, or select it and press **CONNECT** in the drawer that opens beside the grid, which is the same
+command with the password box above it. Keycloak's admin console is at `http://localhost:18080`
+(`admin` / `admin`).
 
 You can also add an SSH key, which is stored in the vault like a host and synced the same way: paste the
 private key, then edit a host and pick that key from its **key** dropdown. From then on that host
@@ -270,13 +271,20 @@ fit 360dp.
 
 Its interface is the **v2 design**: four destinations in a bottom bar — Hosts, Terminal, Keychain and More
 — with snippets, SFTP, S3 buckets, logs and preferences one tap deeper behind the last. Both heads are on
-that design now; the desktop's own v2 is a 190-pixel labelled sidebar in place of the icon rail, a centred
+that design now; the desktop's own v2 is a 190-pixel labelled nav rail in place of the icon rail, a centred
 search box in the titlebar, and session tabs as pills. Its light theme is not built — see
 [`docs/design-import-gaps.md`](docs/design-import-gaps.md) — so the application is dark on both.
 
-Widening the sidebar moved the desktop window's minimum from `880x560` to `1016x574`, which leaves every
+Widening the rail moved the desktop window's minimum from `880x560` to `1016x574`, which leaves every
 screen exactly the width it was designed against.
 
+A third desktop pass has since moved the furniture. The tab strip belongs to the window rather than to the
+terminal: **Vaults**, **SFTP** and **S3** are fixed tabs at its head and open terminals follow them, which
+took SFTP and S3 out of the nav rail — they are the two destinations you stay in while something runs. The
+hosts screen became a grid of cards, groups above and hosts below, with a right-hand drawer for whichever
+host is selected and for both editors; the 268-pixel host sidebar is gone. Text is white rather than the
+design's blue-tinted `#E3E7F4`, and the type scale is a point larger.
+
 File transfer **is** here now, in the shape scoped storage allows: one remote pane and the queue, over
 either an SFTP host or a bucket. There is no local pane, because there is no browsable local filesystem to
 put in one — moving a file *in* from the phone needs the system document picker and is the next piece of