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.

BACKLOG.md

@@ -314,8 +314,9 @@ Sami explicitly stated he wants email auth as an OPTION alongside TOTP, not a re
 - **prerequisite:** DC-048 (shipped).
 
 ### DC-053: Public share links + Tailscale-mediated share — Pro-gated
-- **status:** in-progress
+- **status:** done
 - **owner:** hermes
+- **result:** Shipped as `PROD` commit (this session). Share-store (`src/security/share-store.js`) + share-routes (`routes/share.js`) + 53 tests (24 store + 29 routes, full suite 1372/1372). Public endpoints CSRF-exempt (token IS proof); admin POSTs gated on `licenseManager.isPro()` → 402 PaymentRequired on Free. Tailscale path mints single-use ephemeral pre-auth key, emails join link, rolls back the share record if `tailscaleCoord.createAuthKey()` throws so no orphans leak. Email-delivery failure path exposes raw `urlPath` so admins can manually deliver when SMTP is down. Drift-test parser hardened against quoted-word comments. Public-route drift test registers `routes/share.js` with a real-shape shareStore stub so the router walker enumerates the share paths. **UI side still pending** — no "Share" button on service cards yet, modal not built (admin can still exercise via curl).
 - **details:** Two new feature surfaces behind a Pro license check. (1) **Public share links** — `POST /api/v1/share` creates a signed URL (e.g. `https://status.sami/share/<token>`) for a specific service + a TTL (1h/24h/7d). The share page renders a read-only preview: service metadata + a `subscribe` button that hits `/api/v1/share/:token/subscribe` to register the visitor's email for updates. (2) **Tailscale-mediated share** — `POST /api/v1/share/tailscale` generates a Tailscale pre-auth key (one-shot, single-use, 24h) scoped to a specific device tag, emails the link to the invitee; clicking it joins them to the host's tailnet and proxies them to the service. Both surfaces gated on `licenseManager.isPro()` (DC-052). UI: a "Share" button on each service card, modal with the two tabs.
 - **impact:** The killer Pro feature. "Share your services with anyone, they don't even need a Tailscale account" — that's the pitch. Without this, Pro has no upgrade pull.
 - **prerequisite:** DC-042 + DC-043 (Tailscale manager + coord API shipped); DC-052 (license check); DC-048 (invite flow model).