Workspaces: dogfood fixes — relink memory, consent before seeding, pin skills, clearer link/TUI messages

[anandgupta42]

Bugs found dogfooding the Workspaces pilot (ALTIMATE_WORKSPACE=1) with two users, SSH and HTTPS clones, pilot on and off.

• Relinking a project leaves the previous workspace's memory in open sessions.
• Opening the TUI in a repo a teammate linked uploads local memory before the user chooses Attach or Skip.
• An IDE pin that can't be honoured keeps another workspace's skills loaded.
• link reports success when the memory seed failed.
• With the pilot flag off, link fails with "Failed to change directory to …/link" and exits 0.
• /workspace is a dead end in an unlinked project; no Open in browser or Switch workspace.
• The workspace identity prompt points CLI users at an IDE extension and can't say "not signed in".
• The prompt and docs say warehouse routing ignores the IDE pin (stale since fix(workspace): make the routing section follow the pinned workspace #1357).
• A teammate linking a repo tied to a private workspace gets a false "claimed this project while you were choosing" error.