Run locally like the sibling apps: fixed ports, the pod provider in Docker, the app outside

Festipod now follows the local convention of welcometomyplace, mutual-aid.app
and portejunes: one fixed port pair per app (Festipod defaults: backend 3005,
app 4005; pod provider 3000/5000), overridable in backend/.env and .env.
`make start` runs docker-compose-dev.yml (the local pod provider from images,
Fuseki, Redis, mailcatcher, Arena); the backend and the app run outside Docker
with `cd backend && pnpm dev` and `pnpm dev`. pnpm stays the package manager.

The old docker-compose.yml, which containerized Festipod's own frontend and
backend and could not reach the host's Fuseki and Redis, is gone; portless is
dropped from the dev script, since the backend declares a single OIDC redirect
URI. The local backend runs without a Redis cache, as the sibling apps do. The
e2e suites and validate read the app, backend and pod provider URLs from the
env files instead of hardcoding them.

The deployment and local cookbook leaves record the traps met while resetting
datasets: a dataset re-created under the same name needs a Fuseki restart
(ClosedException otherwise), the anonymous WebACL probe at boot is expected,
and a change of the backend's URL leaves persistent accounts with a
participations collection the new app identity cannot control.

AGENTS.md

@@ -12,7 +12,7 @@ Web app mobile-first où les utilisateurs créent des **points de rencontre** qu
   src/screens/index.ts # Registre d'écrans (utilisé par Storybook)
   ```
 - **Un module n'importe QUE depuis `shared/` — jamais d'un autre module.** C'est l'invariant qui rend l'archi réelle.
-- **Bun-first** : `bun` / `bun install` / `bun test` / `bun build`, jamais node/npm/vite/jest. `bun run dev` (portless, port dynamique ; défaut servi par `bun run start` : 4000).
+- **Bun-first** : `bun` / `bun install` / `bun test` / `bun build`, jamais node/npm/vite/jest. `pnpm dev` (port fixe, `PORT` du `.env` racine, défaut 4005 ; même défaut pour `pnpm start`).
 
 ## Frontière SDK