Run seeds only once (#475)

## Description of the implemented changes
The changes were:
- [ ] Bugfixing
- [x] New Feature
- [ ] Breaking Change
- [x] Refactoring

**Seeds run only on first startup.** On every application start (e.g. `just run`, Docker entrypoint), seed scripts are still invoked, but they exit immediately when the admin user already exists. This avoids duplicate seed data (e.g. join requests), keeps startup fast after the first run, and works the same in dev and production.

## What has been changed?

- **`lib/mv/release.ex`**
  - Added `bootstrap_seeds_applied?/0`: returns whether the admin user (from `ADMIN_EMAIL` or default `admin@localhost`) exists. We check the admin *user*, not the Admin *role*, so we do not skip when only migrations have run (migrations can create the Admin role for the system actor).
  - `run_seeds/0`: if `bootstrap_seeds_applied?()` is true, prints “Seeds already applied (admin user exists). Skipping.” and returns without running bootstrap or dev seeds; otherwise unchanged behaviour.
  - Module docs updated for the new function and the skip behaviour.

- **`priv/repo/seeds.exs`**
  - Ensures the app is started (`Application.ensure_all_started(:mv)`).
  - If `Mv.Release.bootstrap_seeds_applied?()` is true, prints the same skip message and does not run bootstrap or dev seeds; otherwise runs as before (bootstrap + dev seeds in dev/test).
  - Comment at the top updated to describe the skip behaviour.

- **Documentation**
  - `CODE_GUIDELINES.md` §1.2.1: seeds run on every start but exit early when already applied; mentions `bootstrap_seeds_applied?/0`.
  - `docs/admin-bootstrap-and-oidc-role-sync.md`: run_seeds skips when admin user exists; description of `run_seeds/0` updated.
  - `CHANGELOG.md` [Unreleased]: new “Seeds run only when needed” entry under Changed.

## Definition of Done
### Code Quality
- [x] No new technical depths
- [x] Linting passed
- [x] Documentation is added where needed

### Accessibility
- [x] New elements are properly defined with html-tags *(no new UI)*
- [x] Colour contrast follows WCAG criteria *(no new UI)*
- [x] Aria labels are added when needed *(no new UI)*
- [x] Everything is accessible by keyboard *(no new UI)*
- [x] Tab-Order is comprehensible *(no new UI)*
- [x] All interactive elements have a visible focus *(no new UI)*

### Testing
- [x] Tests for new code are written *(existing seeds and release tests cover behaviour; idempotency test still passes when second run skips)*
- [x] All tests pass
- [x] axe-core dev tools show no critical or major issues *(no UI changes)*

## Additional Notes

- **Review focus:** Logic in `Mv.Release` and `priv/repo/seeds.exs`; the “already applied” check is a single DB read for the admin user. On failure (e.g. DB down), `bootstrap_seeds_applied?/0` returns `false`, so seeds run (safe for first deploy).
- **Suggested check:** Run `mix test test/seeds_test.exs test/mv/release_test.exs` to confirm seeds and release behaviour.

Reviewed-on: #475
Co-authored-by: Simon <s.thiessen@local-it.org>
Co-committed-by: Simon <s.thiessen@local-it.org>

CHANGELOG.md

@@ -5,13 +5,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [1.1.1] - 2026-03-16
 
 ### Added
+- **FORCE_SEEDS** – Environment variable. When set to `"true"`, bootstrap (and optionally dev) seeds are run even when the admin user already exists, so you can re-apply changed seed data (e.g. new roles or custom fields) without deleting the admin user.
 - **Improved OIDC-only mode** – Admin can enable “Only OIDC sign-in” in settings; when enabled, direct registration is disabled and sign-in page redirects to OIDC when configured.
 - **Success toast auto-dismiss** – Success flash messages (e.g. “Settings saved”) hide automatically after 5 seconds instead of requiring the user to close them.
 
 ### Changed
+- **Seeds run only when needed** – Bootstrap and dev seeds are skipped on application start when the admin user already exists (`Mv.Release.bootstrap_seeds_applied?/0`). This avoids duplicate data and speeds up startup in dev and production after the first run. Set `FORCE_SEEDS=true` to override and re-run.
 - **Unauthenticated access** – Users who are not logged in are redirected to sign-in without showing a “no permission” message; the message is only shown to logged-in users who lack access.
 
 ### Fixed