Rename project from Nexa to Osias

Renames the npm package (nexa-extension -> osias-extension), the
extension manifest name and Firefox gecko id
([email protected]), the internal runtime message-type
namespace and storage keys ('nexa:...' -> 'osias:...'), the
NexaMessage type, and all remaining Nexa branding in source comments,
UI copy, and CLAUDE.md to match the new osias.trade domain and the
osias-trade GitHub org.

No wire-protocol changes — purely internal naming plus user-facing
strings.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Tn7uDYjTuZEbLPwpEiSCUw

package-lock.json

@@ -1,11 +1,11 @@
 {
-  "name": "nexa-extension",
+  "name": "osias-extension",
   "version": "0.1.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
-      "name": "nexa-extension",
+      "name": "osias-extension",
       "version": "0.1.0",
       "hasInstallScript": true,
       "dependencies": {