fix: manifest author and homepage are blackbeard's, not polkadot{.js}'s

The rebrand renamed the extension but left the manifest's author as
"polkadot.{js}" and its homepage as the upstream GitHub repo. Browsers show
both on the add-on's details page. Package.json authorship stays upstream's:
that is credit for the code, not the extension's identity.

Refs #2, #15

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012uDUodEcRbBwNRi3UCmw8f

packages/extension/manifest_chrome.json

@@ -1,7 +1,7 @@
 {
-  "author": "polkadot.{js}",
+  "author": "blackbeard",
   "description": "A post-quantum wallet for the Quantus Network: ML-DSA-65 and ML-DSA-87 accounts, wormhole balances, and signing for dapps.",
-  "homepage_url": "https://github.com/polkadot-js/extension",
+  "homepage_url": "https://git.lair.cafe/quantus/extension",
   "name": "blackbeard",
   "short_name": "blackbeard",
   "manifest_version": 3,

packages/extension/manifest_firefox.json

@@ -1,7 +1,7 @@
 {
-  "author": "polkadot.{js}",
+  "author": "blackbeard",
   "description": "A post-quantum wallet for the Quantus Network: ML-DSA-65 and ML-DSA-87 accounts, wormhole balances, and signing for dapps.",
-  "homepage_url": "https://github.com/polkadot-js/extension",
+  "homepage_url": "https://git.lair.cafe/quantus/extension",
   "name": "blackbeard",
   "short_name": "blackbeard",
   "manifest_version": 3,