Wire Authelia SSO into Immich, Audiobookshelf, and Beszel

_authelia_provision_oidc_client gains an optional PKCE flag (new 5th
positional arg; every existing caller updated to pass "n", producing an
identical client block to before) — Audiobookshelf and Beszel's own
Authelia integration docs both require require_pkce/pkce_challenge_method,
which Authelia doesn't turn on by default.

immich.sh: _immich_offer_authelia_oidc() is real server-side automation,
not just paste-in instructions — confirmed the exact system-config "oauth"
JSON field names against Immich's own config-file.md and source (not
guessed, closing out the "needs one more verification pass" note this
repo's own CLAUDE.md already had on file). GET/PUT exchange the whole
config object, so it round-trips everything else unchanged. Needs an
admin API key that doesn't exist until first web-UI visit, so it's wired
into both the fresh-install path and the "update" rerun path.

audiobookshelf.sh, beszel.sh: both apps' OIDC config is UI-only (checked
against audiobookshelf.org and beszel.dev directly — no config API or env
var for the provider fields), so their new offers automate the Authelia
side and print exact paste-in values. Beszel also gets a real, separate
DISABLE_PASSWORD_AUTH/USER_CREATION toggle to fully replace its login,
gated behind a warning to register a working account first.

Also adds Audiobookshelf and Beszel as presets in authelia.sh's own
generic "Register another app" menu, and updates CLAUDE.md's OIDC
verification table to match reality (Immich now wired, Audiobookshelf
was wrongly listed as "high-confidence no", Beszel added).

CLAUDE.md

@@ -467,12 +467,14 @@ right (Portainer, ntfy), not general familiarity with the product:
 |---|---|---|
 | `mealie` | Yes — wired up | Pure env vars (`OIDC_AUTH_ENABLED`, `OIDC_CLIENT_ID/SECRET`, `OIDC_CONFIGURATION_URL`), see `_mealie_offer_authelia_oidc()`. Redirect URI is `<BASE_URL>/login`. Needs a `--forwarded-allow-ips` entrypoint override when Caddy-fronted, or the generated redirect URI comes out `http://` even when actually served over `https://` — see the function's own comment. |
 | `actualbudget` | Yes — wired up | Pure env vars (`ACTUAL_OPENID_DISCOVERY_URL`, `ACTUAL_OPENID_CLIENT_ID/SECRET`, `ACTUAL_OPENID_SERVER_HOSTNAME`), see `_actualbudget_offer_authelia_oidc()`. Redirect path `/openid/callback` (matches the existing preset in `_authelia_add_oidc_client()`'s menu). First OIDC login becomes the server owner if none is set yet — Actual's own behavior. |
-| `immich` | Yes, not yet wired up | Real OAuth2/OIDC settings under Administration → Settings, backed by a `system-config` API (GET/PUT) — confirmed the API exists, but didn't confirm the exact request payload shape needed to set OAuth fields specifically. Needs one more verification pass against the live OpenAPI spec before automating; don't guess the payload. |
+| `immich` | Yes — wired up | Real OAuth2/OIDC settings under Administration → Settings, backed by `GET`/`PUT /api/system-config` — confirmed the exact JSON field names against Immich's own `config-file.md` and source directly (the `oauth` sub-object: `enabled`/`issuerUrl`/`clientId`/`clientSecret`/`scope`/`buttonText`, etc.), not guessed. See `_immich_offer_authelia_oidc()`. GET/PUT exchange the *whole* config object (no partial-patch endpoint), so it round-trips everything else — storage template, library settings — completely unchanged; the same shape already proven by `import-photos.sh`'s own storage-template step in this file. Needs an admin API key, which doesn't exist until the user creates their account on first web visit — this offer runs from both the fresh-install path (usually a no-op that first time) and the "update" rerun path, which is the realistic way most people finish this. |
+| `audiobookshelf` | Yes — wired up (Authelia side only) | Checked against audiobookshelf.org's own OIDC docs: config is UI-only (Settings → Authentication), no env var or config API — so `_audiobookshelf_offer_authelia_oidc()` registers the Authelia client (needs PKCE, confirmed via authelia.com's own integration page for it) and prints the exact individual-endpoint values to paste in, since Audiobookshelf wants those rather than a discovery URL. Three redirect URIs: web callback, mobile-redirect, and the `audiobookshelf://oauth` app-scheme callback. |
+| `beszel` | Yes — wired up (Authelia side only) | PocketBase-based; its OAuth2 provider is a PocketBase admin-UI setting (Settings → Auth providers), not an API — checked against beszel.dev directly. `_beszel_offer_authelia_oidc()` registers the Authelia client (also needs PKCE, per authelia.com's Beszel integration page) and prints the paste-in values. Separately offers the real, documented `DISABLE_PASSWORD_AUTH`/`USER_CREATION` env vars to fully replace Beszel's own login — gated behind an explicit warning to register a working account first, since Beszel has no default account and no signup-fallback if that hasn't happened yet. |
 | `jellyfin` | Only via a third-party plugin | No official native OIDC. Community plugins exist (`jellyfin-plugin-sso`, `jellyfin-plugin-oidc`) but are web-UI-only — native mobile/desktop Jellyfin clients can't use them. A bigger lift than an env-var toggle (plugin install via Jellyfin's own plugin repo system); hold off until that's worth doing deliberately. |
 | `homeassistant` | Only via a third-party HACS integration | No native core OIDC as of 2026 (open community discussion asking for it, not shipped). `hass-oidc-auth`/`hass-openid` exist as HACS-installed integrations — same "bigger lift" caveat as Jellyfin. |
 | `portainer` | No (CE) | OAuth/OIDC is a **Business Edition** feature — this repo installs `portainer-ce` (confirmed in `services/portainer.sh`), which doesn't have it. CE's documented path is fronting it with `oauth2-proxy`, i.e. no different from the forward_auth pattern any no-built-in-auth service already uses — not "native OIDC" in the sense this section means. |
 | `ntfy` | No | Checked ntfy's own config docs directly — no `auth-oauth2-*` keys exist. Only basic auth + access tokens + ACLs. (Worth a re-check on a future ntfy release if this matters to you — this class of feature does get added to self-hosted tools over time.) |
-| `emby`, `audiobookshelf`, `meshcentral`, `traccar`, `uptimekuma`, `filebrowser`, `wg-easy` | Not individually re-verified | High-confidence no, based on general familiarity with each product rather than a fresh doc check this pass (unlike everything above, which was actually checked and in two cases contradicted assumption). Verify before wiring any of these in, the same way the checked ones were — don't extrapolate from this table's pattern.
+| `emby`, `meshcentral`, `traccar`, `uptimekuma`, `filebrowser`, `wg-easy` | Not individually re-verified | High-confidence no, based on general familiarity with each product rather than a fresh doc check this pass (unlike everything above, which was actually checked and in two cases contradicted assumption). Verify before wiring any of these in, the same way the checked ones were — don't extrapolate from this table's pattern.
 
 **No built-in auth — should be protected:**
 `magicmirror`, `wolf-pair`, `js99er`, `drum-rhythm-game`, `iopaint`,