BACKLOG + CHANGELOG: mark DC-049 done

Track record of the auth-gate UI work plus the historical delta from
DC-046/047/050/049 commit chain. No code changes.

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **Pluggable auth UI — DC-049.** `status/js/auth-gate.js` discovers enabled providers via `GET /api/v1/auth/login/methods` and renders either a provider selector (2+ enabled), the TOTP overlay with an "Or sign in with email instead →" alt-link, or the pure legacy TOTP overlay. Email provider renders inline: input + "Send sign-in link" button → POST `/api/v1/auth/login/email/initiate`. Coordination flag `window.__dc_049_handled` eliminates flicker on multi-provider installs. New SW cache hash `dashcaddy-shell-c550d0b371`.
 - **Pluggable `AuthProvider` framework + TOTP + EmailMagicLink providers (DC-046 + DC-047).** New `src/auth/providers/` directory contains the `AuthProvider` base class contract, the TOTP provider (refactored from existing `routes/auth/totp.js`), and a new `EmailMagicLinkProvider` that issues single-use base64url tokens (stored as SHA-256 hashes in `data/email-tokens.json`), sends via the existing nodemailer config (or logs to console + `log.info('email magic link issued')` in dev fallback). `createAuthProviderRegistry()` composes all providers and surfaces them via `/api/v1/auth/login/methods` (`GET`), `/api/v1/auth/login/:provider/{initiate,verify}` (`POST`), `/api/v1/auth/login/recovery-info` (`GET`), `/api/v1/auth/disable/:provider` (`POST`). Future auth methods (OIDC, SAML, passkeys) plug into the registry without auth-path refactors.
 - **`platform-paths.assertSafe()` — DC-046 hardening.** Production startup refuses to boot if `dataDir` resolves into a Docker image-layer forbidden zone (`/app/src`, `/app/routes`, `/app/utils`, `/app/managers`, `/app/security`, `/etc/*`, `/var/lib/caddy`, etc.). Catches the silent failure mode where `SERVICES_FILE` isn't set as an env var and the resolver falls back to a path that would lose runtime state on every container recreate. Bypassed with `SKIP_DATA_DIR_GUARD=1` for emergency legacy setups.
 - **`platform-paths.isMountedCheck(dir)`.** Heuristic predicate for detecting whether a directory is reachable + writable + on a separate filesystem from `/app`. Used by `start.sh` migration step to no-op safely on fresh installs.