Compliance: error-row and repo-page polish found while checking

Found while checking Task 6681's matrix on a live stack (desktop 1280, phone 390). Suggestions: 1. A single-repo project's repo page shows no scan-error detail. Only multi-repo sections render `target_error`. Show the run's error, as a short phrase plus its detail, beside the Scan error badge on the repo page too. 2. After a row's Rescan is clicked, the button only greys out until the next poll. Say "Rescanning…" on the button so the click is visibly acknowledged. 3. On the phone card the Level "—" sits alone before the stack label and reads as stray punctuation. Hide the dash on a row with no level, or label it ("No level"). 4. A row with no `compliance:edit` (e.g. "Could not start the run") gives no next step. Add a short "Ask an editor to rescan" hint, or link the repo page. Out of scope: scan time bound, Stop scan's behaviour, rule content, packs, the Architectural Guard, docs pages. Done means: each item shipped with a vitest test; the matrix and repo page rendered and checked at 1280 and 390; `./dc check full` green.

Shipped all 4 items with vitest tests: repo-page error phrase and detail, Rescanning… ack, no stray card dash, ask-an-editor hint. Visual check at 1280/390 passed. Local full gate rerun was OOM-killed; merge lane gated and merged PR #5638. Follow-ups in draft #6755.