feat(ui): separate dev info into a Diagnose view, declutter the scan workspace

Reworks the UI so the Scan tab shows only core actions and all developer /
diagnostic surfaces live in one dedicated view.

- New "Diagnose" nav view. ScanView stays mounted for scan|diagnose (the scan
  controller state persists across the switch) and renders either the clean
  workspace or the new DiagnosticsView by mode.
- DiagnosticsView consolidates runtime/rights, grid detection, learning + data
  staleness, fingerprint, auto-scan counters, the automation log, the dev-output
  toggle, the Demo-Daten action, and the raw crops/OCR/confidence dump. Reuses
  the existing diagnostics/details model hooks.
- Scan workspace decluttered: removed the Scanner Diagnose button and the Details
  button, dropped the rules/grid/mode dev fields from the result brief and capture
  meta, shortened the topbar headline, and moved Demo-Daten out of the topbar.
- Removed the now-dead ScanDiagnosticsModal / ScanDetailsModal components (their
  content moved into the view); metrics grid hidden on the Diagnose view.
- Added dev:web script + .claude/launch.json for browser preview.

Verified in the browser preview (both views render, no console errors); 120
tests + build green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package.json

@@ -8,6 +8,7 @@
   "scripts": {
     "predev": "powershell -NoProfile -ExecutionPolicy Bypass -File scripts\\kill-stale-instances.ps1 && tsc -p tsconfig.electron.json && copy electron\\preload.cjs dist-electron\\preload.cjs",
     "dev": "concurrently -k \"vite --host 127.0.0.1\" \"wait-on tcp:5173 && cross-env VITE_DEV_SERVER_URL=http://127.0.0.1:5173 electron .\"",
+    "dev:web": "vite --host 127.0.0.1",
     "dev:admin": ".\\dev-admin.cmd",
     "build": "tsc && vite build && tsc -p tsconfig.electron.json && copy electron\\\\preload.cjs dist-electron\\\\preload.cjs",
     "preview": "vite preview --host 127.0.0.1",