DC-053: Public share links + Tailscale-mediated share (Pro-gated)

- Share-store: HMAC-signed tokens bound to serviceId+kind, persistent
  signing secret in dataDir/.share-secret, atomic writes, auto-prune
- Routes: admin endpoints gated on licenseManager.isPro() (402 Free);
  public endpoints CSRF-exempt (token IS proof)
- Tailscale path: mints single-use ephemeral pre-auth key, emails
  join link, rolls back share record if createAuthKey throws
- Email-failure path: exposes urlPath for manual delivery fallback
- 53 new tests (24 store + 29 routes), full suite 1372/1372
- Drift-test parser hardened against quoted-word comments
- share-store dataDir resolver handles Proxy/function values

CHANGELOG + BACKLOG updated.

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- **Public share links + Tailscale-mediated share — DC-053.** Pro-tier feature behind a 402 PaymentRequired gate on Free installs. New `src/security/share-store.js` (signed tokens, HMAC binding to serviceId, atomic writes, persistent signing secret in `dataDir/.share-secret`, auto-prune, defensive dataDir resolver). New `routes/share.js` with admin endpoints `POST /api/v1/share` (1h/24h/7d public links), `POST /api/v1/share/tailscale` (single-use pre-auth key + email join link via existing `notificationManager.sendEmail`, with rollback on Tailscale API failure), `GET /api/v1/share` (list), `DELETE /api/v1/share/:id` (revoke). Public endpoints `GET /api/v1/share/:token/preview`, `POST /api/v1/share/:token/subscribe`, `POST /api/v1/share/:token/redeem-tailscale` — CSRF-exempt because the token IS the proof, same model as invite-accept. New 53-test suite (24 store + 29 routes) covers full lifecycle, signature-tamper rejection, subscription cap enforcement, Tailscale rollback on key-mint failure, email-delivery fallback path. Drift-test parser hardened against quoted-word comments. Full suite 1372/1372.
 - **Multi-user bootstrap + admin invites — DC-048.** Opt-in via `siteConfig.authProviders.email.enabled = true`. Single-user TOTP-only installs see zero behavior change. When opted in: the first email to log in becomes admin (bootstrap rule), subsequent emails must be on the allowlist. New `src/security/user-store.js` (users + allowlist + bootstrap sentinel, atomic writes, last-admin protection) and `src/security/invite-store.js` (single-use tokens, SHA-256 hashed on disk, TTL, auto-prune). New `routes/auth/admin.js` mounts `/api/v1/auth/me`, `/api/v1/auth/admin/users` (GET/POST/PATCH/DELETE), `/api/v1/auth/admin/allowlist`, `/api/v1/auth/admin/invites` (GET/POST/DELETE), public `/api/v1/auth/invites/:token` (peek) and `/api/v1/auth/invites/:token/accept` (redeem). EmailMagicLinkProvider `verify()` and TOTP `verify()` tag `req.user` for audit attribution; TOTP bootstraps a `system@totp.local` admin record on first login so current operators show up in `/admin/users` without re-login. Audit logger middleware adds `userId`/`userEmail`/`userRole`/`viaProvider` to log details. New admin UI in `status/js/admin.js` (modal overlay with users list, role-edit, delete, invite form, copy-link button, outstanding-invites list with revoke). "Admin" button auto-injects into the top bar when `/me` returns `isAdmin: true`. 35 new tests; full suite 1298/1298.
 - **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.