fix(ab-connect): fail loudly on a stale sessionId instead of routing to a random tab (issue #8.1)

handleForwardCdpCommand fell through to anyConnectedTab() when a
daemon-supplied sessionId didn't map to an attached tab, so eval/screenshot/
network silently ran on an arbitrary tab — the root of "eval ran on the
wrong page, no warning" and the blank-screenshot-after-restart symptom.

Now: a provided sessionId/targetId MUST resolve to a real tab or the command
throws an actionable error ("stale sessionId … re-open your target URL").
anyConnectedTab() is only used for genuinely browser-level commands that
specify neither. Manifest 0.4.1 → 0.4.2 (needs a Chrome Web Store republish
for installed users to pick this up).

extensions/ab-connect/manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "agent-browser-stealth",
-  "version": "0.4.1",
+  "version": "0.4.2",
   "description": "Let agent-browser drive your logged-in Chrome \u2014 install once, no token, no per-use confirmation.",
   "key": "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA6vQIyscGIPYPZdSpPwPL0+0gxUROyRgCpmvCSDoc8XUm4qm97VbKnD9Ijc1lV22lNWZtE78gaRjt6BeSfuMgnBymnhLKjN1gU6AI5QUU0mrJyeHdWKvrKQR5FmsM2A7Xr1ykE2SiiS8zNUS3Y/6O5l+Nva7wrVy6E4a2dkBVQkOsu+DV+nEZvhIyuDY5D5SPXqNwUTWTaglwj5mjvHz36xSwCWlPmrtJ+ED0AUyrb2z4GIOmvk4kqtBVrh/UD058klLo4CkYOnIybB5aV6WYuwarfPY4bF/dLggPem+ewLNTUNBuwrxj/A4nUv0LJTuRO8rR7f8WR9qnRCY0Ic5saQIDAQAB",
   "icons": {