docs: sync every doc surface with the v1.63 release

/document-release audit (4-lane, all claims verified against branch code):

- README: gstack-egress + gstack-context-bill rows in the standalone-binaries
  table; Privacy & Telemetry gains the receipted-egress bullet (attempted-
  egress framing per the shipped threat model).
- ARCHITECTURE: /health is liveness-only, POST /extension-token endpoint row
  + bootstrap mechanics paragraph; new Egress receipt ledger subsection under
  Security model; eval persistence covers the sharded runner, GSTACK_EVAL_DIR,
  and the finalized-run baseline rule.
- CLAUDE.md: sharded test scripts in Commands; sharded semantics in the
  detached-evals section; PTY skill seeding in the hermetic section; egress
  invariant block beside the other server-egress invariants; catalog-budget
  ceiling beside the 160KB token ceiling; project-tree entries for
  lib/egress-receipt.ts, lib/context-bill.ts, scripts/test-paid-shards.ts.
- CONTRIBUTING: seedSkills + live-tree seeding in the hermetic paragraph;
  sharded runner in detached runs; catalog-budget in the Tier 1 list.
- BROWSER: extension token bootstrap section, tunnel egress receipts section,
  identity-pin migration note in manual install.
- REMOTE_BROWSER_ACCESS: tunnel-start receipt bullet in the security model.
- gbrain docs: /sync-gbrain + brain-sync egress-receipt behavior documented;
  dead consumer-token instructions removed (consumer machinery deleted this
  release); new fail-closed refusal added to the error catalog.
- CHANGELOG: measured-vs-ceiling catalog numbers, contributor notes for the
  external-service tier move and the PTY single-line AskUserQuestion parser,
  release date.
- TODOS: /health token-distribution TODO resolved by this release, removed;
  port-wave follow-up sections re-labeled to the shipped version.

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

docs/REMOTE_BROWSER_ACCESS.md

@@ -179,6 +179,7 @@ Each agent owns the tabs it creates. Rules:
 - **Path traversal guarded** on `/welcome` — `GSTACK_SLUG` must match `^[a-z0-9_-]+$` or falls back to the built-in template.
 - **SSRF guards** on `goto`, `download`, and scrape paths — validates URL target against a localhost/private-range blocklist.
 - **Tunnel surface denial logging.** Every rejection on the tunnel listener (`path_not_on_tunnel`, `root_token_on_tunnel`, `missing_scoped_token`, `disallowed_command:*`) is appended to `~/.gstack/security/attempts.jsonl` with timestamp, source IP, path, method. Rate-capped at 60 writes/min.
+- **Egress receipt on tunnel start (v1.63+).** Every tunnel session open writes a hash-chained receipt (sink `browse-tunnel`) to `~/.gstack/security/egress.jsonl` BEFORE ngrok forwards anything. Fail-closed: if the receipt can't be written, the tunnel refuses to start. Audit with `bin/gstack-egress list` / `bin/gstack-egress verify`.
 - All agent activity is logged with attribution (clientId).
 
 **Known non-goal (tracked as #1136):** on Windows, the cookie-import-browser path launches Chrome with `--remote-debugging-port=<random>`. With App-Bound Encryption v20, a same-user local process can connect to that port and exfiltrate decrypted v20 cookies — an elevation path relative to reading the SQLite DB directly. Fix direction is `--remote-debugging-pipe` instead of TCP.