fix: harden frame observation and unblock supported Drive tabs

Audit follow-ups on the same-origin frame walk:
- prune detached frames from the load-hook set so ad/SPA frame churn
  no longer grows it for the page's lifetime
- hook load on nested frames, not just top-level ones
- re-observe from scratch after a frame reload instead of leaving the
  replaced document's tree registered
- reset the frame registry when the heartbeat error path disconnects

Also: a broad parent domain in the blacklist no longer hides a host with
its own supported player path (drive.google.com behind google.com), while
an exact user entry for that host still filters it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

shared/blacklist.js

@@ -179,6 +179,15 @@ export const BLACKLIST_DOMAINS = [
     'skribbl.io'
 ];
 
+/**
+ * Hosts KoalaSync supports through a site-specific player path. A broad parent
+ * domain in the list (e.g. 'google.com') must not hide them from tab selection.
+ * An exact entry for the host itself still filters it, so users stay in control.
+ */
+export const BLACKLIST_SUFFIX_EXCEPTIONS = [
+    'drive.google.com'
+];
+
 export const CUSTOM_BLACKLIST_STORAGE_KEY = 'customBlacklistDomains';
 export const MAX_BLACKLIST_DOMAINS = 500;
 
@@ -246,5 +255,9 @@ export function isUrlBlacklisted(rawUrl, domains = BLACKLIST_DOMAINS) {
         return false;
     }
 
-    return domains.some(domain => hostname === domain || hostname.endsWith(`.${domain}`));
+    return domains.some(domain => {
+        if (hostname === domain) return true;
+        if (!hostname.endsWith(`.${domain}`)) return false;
+        return !BLACKLIST_SUFFIX_EXCEPTIONS.includes(hostname);
+    });
 }