feat(claude): Settings → Claude per-workspace account picker (T-482 part 1)

A custom settings control under the Claude category: a dropdown of the
registered accounts plus Default. Picking one binds (or unbinds) this
workspace via the AccountRegistry and publishes set/unset on
accountActionChannel — the same channel the CLI verbs use, so the session
respawns onto the account (T-480) and the IDE lock re-syncs (T-479). It reads
live off the shared settings notifier, so a CLI `account set` updates the
dropdown too. Empty states cover no-workspace and no-accounts, each pointing at
the CLI.

Registry writes set the in-memory binding synchronously then flush, so the
control publishes the bus event before the disk write completes.

Part 2 (the global Accounts registry CRUD list + sign-in probe) is still open
on T-482. en/nl strings added; widget test covers the states + bind/unbind.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -18,6 +18,9 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Added
 
+- **Settings → Claude → Account picker.** A per-workspace dropdown binds this
+  repo to a registered Claude account (or Default); switching respawns the pane
+  onto it. (T-482, epic T-476)
 - **Per-repo Claude accounts — `clide claude account` verbs.** Manage named
   Claude config dirs and bind one per workspace: `add`/`list`/`set`/`unset`/
   `remove [--purge]`. `set`/`unset` respawn the workspace's Claude pane(s) onto