feat: decaveat Phase 2 — subscription->tier data source + robust client signing

Caveat 2 (premium sub had no data source) -> RESOLVED:
- src/services/subscriptionService.js: resolves a premium tier by npub. Two
  sources, both optional (absent => null => unchanged): PREMIUM_NPUBS operator
  allowlist (npub1/hex[:tier]) works TODAY with zero backend dependency, and an
  optional SMIRK_PREMIUM_STATUS_URL HTTP endpoint for full automation. Cached.
- identityService.entitlementsForUser populates user.subscription_tier from it
  (by smirk_public_key) before the snapshot, so an active sub unlocks cosmetics.
  (The Smirk backend's /premium/status is self-only, so a by-npub service lookup
  is the one remaining backend addition for full automation — documented.)

Caveat 1 (client signing was bare scaffold) -> HARDENED:
- html/js/smirkChatSign.js now does the Nostr-scope-grant retry (sign first; on
  NOT_AUTHORIZED, getNostrPublicKey() once + retry), same as SmirkAuth — so a
  returning user signs with one approval instead of silently falling back. Still
  feature-detected + graceful. A real Smirk wallet click is the last confirm.

Docs updated (MONETIZATION.md, CHAT_AND_NOSTR.md). Tests: +6 (allowlist hex/npub1,
HTTP active/inactive+cache, identityService unlock, non-premium unchanged).
Suite 57 suites / 413 tests green.

html/js/smirkChatSign.js

@@ -8,6 +8,21 @@
     // unavailable or declined — in which case the caller falls back to the normal unsigned send.
     // Feature-detected end to end, so it's a no-op (always false) until the page has a connected
     // Smirk wallet; wiring it into a send site is therefore always safe.
+    // Sign an event, granting the Nostr scope on demand. Signing FIRST means a returning user
+    // (scope already granted for this origin — e.g. from the game's NIP-98 login) gets a single
+    // approval; only a first-time origin hits NOT_AUTHORIZED and needs the one-time scope grant.
+    // Same pattern as SmirkAuth (html/js/network/smirkAuth.js).
+    function signWithScope(smirk, tmpl) {
+        return Promise.resolve()
+            .then(function () { return smirk.signNostrEvent(tmpl); })
+            .catch(function (err) {
+                var needsScope = (err && err.code === 'NOT_AUTHORIZED')
+                    || /nostr scope|getNostrPublicKey/i.test((err && err.message) || '');
+                if (!needsScope || typeof smirk.getNostrPublicKey !== 'function') throw err;
+                return smirk.getNostrPublicKey().then(function () { return smirk.signNostrEvent(tmpl); });
+            });
+    }
+
     function smirkChatSign(socket, text, tag) {
         try {
             var smirk = root.smirk;
@@ -18,7 +33,7 @@
                 tags: [['t', tag || 'wowngeon-global']],
                 content: String(text)
             };
-            return Promise.resolve(smirk.signNostrEvent(tmpl)).then(function (signed) {
+            return signWithScope(smirk, tmpl).then(function (signed) {
                 if (!signed || !signed.id || !signed.sig || !signed.pubkey) return false;
                 socket.emit('chat_signed', { event: signed });
                 return true;