Replace stub wallet keypair with real Phantom sign-in

Auth now goes through an actual connected Solana wallet instead of a
locally-generated ed25519 keypair. Phantom's window.solana provider
is only reachable from a page's own JS world, not an isolated-world
content script, so this adds a second world:'MAIN' content script
(wallet-bridge.content.ts + wallet-bridge/inject.ts) that talks to
window.solana directly and relays to the isolated world via window
CustomEvents (wallet-bridge/relay.ts), matched by request id.

wallet-connect.ts orchestrates: try a silent onlyIfTrusted connect on
load; if that fails, show an on-page banner (wallet-bridge/banner.ts)
whose click handler is what actually calls connect() -- Phantom
requires a real user gesture for the approval popup on a first-ever
connect, which a click relayed from the extension popup wouldn't
count as by the time it reaches the wallet.

background/wallet-auth.ts runs the REST auth flow (nonce -> ask the
tab's content script to sign it -> verify -> store session token)
once a wallet reports connected. ws-client.ts no longer force-retries
with a known-bad token on auth failure; it calls onAuthExpired
instead (which clears the token and prompts a silent wallet
reconnect) and exposes reconnectNow() so background.ts can
short-circuit the backoff wait once a fresh token exists.

identity.ts and its tweetnacl dependency are gone -- no more stub
signer.

Untested against real Phantom (no browser automation available this
session) -- flagged in CLAUDE.md as needing manual verification,
along with a note that world:'MAIN' needs Firefox 128+.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YXiHuScXrjxBh7yFGAPq3B

package.json

@@ -24,7 +24,6 @@
     "@wxt-dev/module-react": "^1.2.2",
     "bs58": "^6.0.0",
     "react": "^19.2.8",
-    "react-dom": "^19.2.8",
-    "tweetnacl": "^1.0.3"
+    "react-dom": "^19.2.8"
   }
 }