feat: live deployment with automated acceptance checklist (phase 13)

- APP_INTERNAL_URL: in-network base URL for §5.2 callbacks and signed
  attachment URLs handed to the external services (compose: http://app:8787)
- work-performer image runs as the node user with ~/.claude mounted into
  /home/node — the claude CLI refuses --dangerously-skip-permissions as root
- scripts/acceptance.sh: re-run-safe live verification of the §13 checklist
  (demo import within one poll, subdivide sum=1 + editable, extend sibling,
  publish/bounty math, decline/claim/approve, changes-requested loop,
  approval award in metrics, unassign, AI job through real Claude Code with
  signed idempotent callback, breaker independence between the two services)
- README/DECISIONS: sudo HOME gotcha, internal URL, non-root performer

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

.env.example

@@ -1,6 +1,9 @@
 # --- core ---
 # Set APP_BASE_URL to the public https URL when behind the reverse proxy.
 APP_BASE_URL=http://localhost:8787
+# In-network address external services use to call back into the app.
+# docker-compose.yml sets this to http://app:8787; defaults to APP_BASE_URL.
+#APP_INTERNAL_URL=
 # Comma-separated CIDRs of trusted reverse proxies, e.g. 172.16.0.0/12,10.0.0.0/8.
 # Empty = trust no proxy headers.
 TRUSTED_PROXY_CIDRS=