docs(plan): add Fase 16 — loading spinner (MVP2 reopened to 8 fases)

Adds a tiny planned-phase doc for visual feedback during async operations.

- Single SVG-circle Spinner.svelte component, three sizes (sm/md/lg = 16
  / 24 / 40 px), color via currentColor (theme-aware), motion-reduce-aware,
  role="status" + sr-only m.loading() for a11y.
- Integration at 5 existing sites that already render m.loading() text or
  own a `loading` flag: auth splash, /search, /notes/archive,
  CreateCollectiveModal "creating" state, /collective/manage sub-sections.
- 5 unit + 3 e2e tests planned. No DB migration. No new Paraglide strings.

Rebrand: MVP2 reopens from 7/7 ✅ to in-progress 7/8 ✅. Headers in fases
9–15 bump "·N/7" + "fases 9 → 15" to "·N/8" + "fases 9 → 16". README +
CLAUDE.md updated.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plan/fase-9-polish-dark-mode.md

@@ -1,6 +1,6 @@
 ### Fase 9 — Polish + Dark Mode
 
-**MVP2 · 1/7.** Primera fase del ciclo MVP2 (rama `mvp2`, fases 9 → 15).
+**MVP2 · 1/8.** Primera fase del ciclo MVP2 (rama `mvp2`, fases 9 → 16).
 
 **Estado: ✅ Completada (2026-05-18). Ver `docs/history/fase-9-polish-dark-mode.md` para detalles + paleta definitiva. 41 tests nuevos: 8 user_theme pgTAP, 12 sync_conflicts pgTAP, 4 sync-conflicts integración, 3 SC unit, 8 theme unit, 3 theme E2E, 3 reading-width E2E. WebKit specs (2 nuevos) gated en `RUN_WEBKIT=1`.**