Console gaps met while verifying provider lanes

Itemized suggestions noticed while running provider-lane checks on app.dev.jaah.ai (Task 9008): 1. **Customer › Overrides saves all sections at once, and one invalid value blocks every other section.** Gmind's Limits › Cron minimum period holds 1 s (minimum 10), so toggling Features › ACP registry / Jaah AI cannot be saved, and the Features view gives no reason. Save each section on its own, or name the blocking field on the section being edited. 2. **New task has no account picker.** Forcing one lane (e.g. an imported or a specific API-key account) means disabling every other account of that provider and restoring them afterwards. Offer an optional Account choice under Advanced. 3. **Audit › Sessions does not show which account a session ran on.** Show the account name on the row or its detail. 4. **Antigravity chat cannot steer a single-turn run.** Send is disabled mid-turn ("takes a new message only between turns"), so a short run never accepts a steer. Queue the message and deliver it at the next turn boundary. 5. **The chat pane's Terminal tab answers 502 on a live ACP session** (`/api/console/<project>/<slot>/open`), with "The terminal can't take over a live chat session yet". Hide the tab while the chat owns the session, or say so without a failed request. Out of scope: changing how sign-in works; NodeLink token sharing; the ACP transcript/usage gaps already filed (#8858, #8859). Done means: - Each item above is fixed, or explicitly declined with a reason, and the fix is checked in the console at desktop and 390px.

PR #6658 merged (e30e5fb). Fixed four gaps: a stale Overrides value no longer blocks other sections; Sessions shows the account; mid-turn chat messages queue; Terminal is disabled or hidden on a live chat. Account picker already shipped (9011). Quick gate and tests green; checked at 1440 and 390px. Deploy superseded by a newer run.