Merge branch 'claude/team-key-share-rotate-4b2619'

Two conflicts, and the second is worth recording. main's M4 bullet gained the
Android signing decision while this branch rewrote the M5 line either side of it;
both are kept.

The other is an ADR number collision: two sessions each took 0010, one for vault
key rotation and one for Android distribution, and both are now on main. ADR
numbers are identifiers — "see ADR 0010" appears in code comments as well as in
prose — so leaving two would make every such reference ambiguous. The rotation
ADR landed first and is referenced from crypto.md, the gaps document, ADR 0009
and the sync code; the Android one is referenced from README and android-port.md.
So the later and cheaper one moves: 0010-android-distribution.md is now ADR 0011,
with its title and both references updated. Nothing about either decision changes.

docs/design-import-gaps.md

@@ -413,6 +413,7 @@ answerable by anybody willing to create a team first. It simply gets claimed soo
 | Sharing an item | client | `VaultSession.ShareVaultAsync`: verify the recipient's key against the key log, wrap, sign, record. The server stores the wrap and the signature and can check neither. One grant per generation the sharing client holds, so a recipient can read a rotated vault's history and not only what happens next. |
 | Adding a member shares the team's vaults | client | Adding somebody wraps every team vault the adding machine can open to them, as part of the add rather than as a button to remember. Membership and a key are still two acts on two machines; the client just performs both. A vault this machine holds no key to is skipped and named. |
 | Removing a member rotates the vaults | server + client | `POST /api/v1/vaults/{id}/rekey` advances the generation and records the caller's new grant in one transaction — the server contributes the moment and no cryptography. The client then wraps the new key to the members who remain. Grants for earlier generations are kept, or the vault's stored items would become unreadable to everybody. See [ADR 0010](adr/0010-vault-key-rotation.md). |
+| Re-sealing a rotated vault's stored items | client | `VaultResealer`, the last step of a rotation: every item is opened and the same plaintext sealed again under the new key, in batches, against the version the server holds. The plaintext is never decoded, so an item written by a newer client crosses a rotation untouched. Resumable, because a vault at mixed generations is readable — a pass that stops half way leaves a working vault and is re-run. A change queued before the rotation is re-sealed by the push path instead, so nothing reaches the server under a superseded key at all. |
 | Pending invites, and withdrawing one | server | A `team_invitation` row per (team, address), listed beside the members it is about and withdrawable until it is taken up. It becomes a membership when an account with that address signs in — **and only if the access token asserts `email_verified`**, because membership is authorisation and an invitation anybody could take by naming somebody else's address is a way in. Fourteen days, because an address that is reassigned would otherwise carry a standing offer to whoever holds the job next. |
 | Ownership transfer | server | `POST /api/v1/teams/{id}/owner`, owner only. One transaction: the named member becomes owner and the outgoing owner becomes an admin. Not two role changes — ownership is sole, so promoting first leaves the team owned twice and demoting first leaves it owned by nobody. The outgoing owner is demoted rather than removed, because removing them would revoke their vault key grants and rotate every team vault, which is a far larger act than the one being asked for. |
 | `LAST ACTIVE` | server | Real, and coarse on purpose. `UserAccount.LastSeenAtUtc` is now refreshed on ordinary authenticated requests, at most once per account per hour: writing it per request would put an UPDATE on the hot path of every authenticated call and start losing races on `user_account`'s own concurrency token. So the column answers "this week or not", which is the granularity the question is actually asked at, and is shown coarsely rather than to the minute. |
@@ -426,7 +427,6 @@ answerable by anybody willing to create a team first. It simply gets claimed soo
 | The invitation mail, and **resend** | server | An outbound mail path: an SMTP configuration, a template, a bounce story and a deliverability problem, none of which this server has. | **Nothing is sent, and the interface says so.** An invitation is a standing instruction rather than a message — the next account to sign in with that address joins the team — so there is no token, no link, and nothing to resend. Telling somebody to sign in is done over a channel this server does not carry. A link nobody can deliver would be worse than no link. |
 | Archiving a team that owns vaults | — | Nothing that would be safe. A team vault resolves through membership, so archiving would take those vaults away from everybody holding a key, silently, including the caller — and nothing in this product deletes a vault, so there is no sequence of calls that turns the refusal into a success. | Refused, with `team-not-empty` and a count of the vaults in the way. A stated limit rather than a coming feature, for the reason the SFTP layer refuses a recursive delete: a refusal is visible and a quiet removal is not. |
 | `SSO · OIDC · okta.dodotech.dev` | server | Per-team SSO. Authentication is one global JWT scheme bound to one authority. | Omitted. |
-| Re-sealing a rotated vault's stored items | client | Re-wrapping every item's data key under the new vault key, in batches, which only a client holding both keys can do. M5. | The rotation itself ships — see the row above. Existing items keep the generation they were sealed under and stay readable, because every member keeps the keys they were granted. What is outstanding is closing the gap where a departed member's copy of the old key would still open old ciphertext they later obtained. |
 
 > **The trap this document warned about is still a trap.** `GET /api/v1/meta` advertises
 > `features: ["teams"]` *unconditionally* (`MetaEndpoints.cs`). It was meaningless when nothing implemented