feat(realtime): full Fase 2b.0 test suite + infra hardening

Extend the 2b.0 red-phase coverage: presence, RLS isolation, offline-queue
contract, and Playwright scaffolds for the shopping-session UX. Only the
presence test is blocked on an upstream Realtime bug (documented below); all
other Realtime paths are proven end-to-end.

Tests
- realtime-postgres-changes.test.ts: now uses afterEach socket disconnect
  (Vitest singleFork kept Phoenix sockets alive between files, leaking state)
- realtime-isolation.test.ts (new): R-I-01 David (guest, same collective)
  receives events; R-I-02 Eva (non-member) receives NONE — RLS is enforced
  server-side per subscribed JWT
- realtime-presence.test.ts (new, describe.skip): two-client roster + leave
  assertions ready, gated on upstream bug
- sync-queue.test.ts (new, describe.skip): 7 placeholders pinning the
  apps/web/src/lib/sync/queue.ts contract (Q-01..Q-04 enqueue / in-order
  flush / retry; F-01..F-03 online-event flush + last-write-wins)
- apps/web/tests/e2e/{session,realtime,offline}.test.ts (new, describe.skip):
  S-01..S-03, R-E-01, R-E-02, O-01, O-02 pinning the Modo Compra UI contract
- vitest.config.ts: fileParallelism=false, drop singleFork so each file gets
  a fresh worker fork — prevents RealtimeClient singleton leakage

Infra
- db-init/00-role-passwords.sh: pre-create `realtime` schema with
  AUTHORIZATION supabase_admin. Realtime's per-tenant migrator creates tables
  INSIDE the schema but does not create the schema itself; without this the
  first tenant connect fails with "schema realtime does not exist"
- docker-compose.dev.yml: adopt the upstream supabase/supabase Realtime env
  shape — SEED_SELF_HOST=true + RUN_JANITOR=true + RLIMIT_NOFILE=10000 +
  drop the custom `command: eval seeds` (that bypasses the normal supervisor
  startup and was observed to cause GenServer crashes under load).
  Version pinned to v2.76.5 to match the official docker-compose.

Known upstream bug
- Realtime v2.76.5 and v2.83.0 both crash on presence_diff:
  `(UndefinedFunctionError) RealtimeChannel.handle_out/3 is undefined`.
  postgres_changes + isolation unaffected (they don't traverse handle_out).
  Presence tests stay `describe.skip` until a fixed upstream is released.

Totals: 59 Vitest passed (+ 9 skipped awaiting implementation/upstream),
16 pgTAP, 15 Playwright (+ 7 E2E scaffolded for 2b UI) = 90 green.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -8,7 +8,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 ## Project Status
 
-**Fase 0 complete. Fase 1 complete. Fase 2a complete. Fase 2b — Realtime infra prep done and R-series tests green. Full test suite green (57 Vitest + 16 pgTAP + 15 Playwright = 88 tests). ✅**
+**Fase 0 complete. Fase 1 complete. Fase 2a complete. Fase 2b — Realtime infra prep done, R-series (postgres_changes + isolation) green, presence blocked by upstream Realtime bug. Full test suite: 59 Vitest passed (+ 2 presence + 7 sync-queue skipped awaiting implementation/upstream fix) + 16 pgTAP + 15 Playwright (+ 7 E2E scaffolded for 2b UI) = 90 green. ✅**
 
 - `README.md` — full development plan, confirmed tech stack, Justfile reference, and technical warnings
 - `analysis/analisis-funcional.md` — complete functional specification (domain model, use cases, data models, business rules)