feat: Sign in with OTM, health, changelog, tides beacon, Ideas — first OTM release (0.4.0)

app/otm.py is the Python port of pickup's ticket verifier (HS256, mandatory
exp, audience check, alg only read to reject, never raises) plus a signed
session cookie and an in-memory single-use jti guard. portable.py gates every
route but PUBLIC_PATHS behind a session and fails CLOSED (503) with no secret
— it is a fetch proxy. /api/health reports the version, /changelog renders
CHANGELOG.md, the footer carries version/sign-out/Ideas, tides beacon from
TIDES_HOST/TIDES_SITE_ID. Dockerfile: OTM labels + HEALTHCHECK. 17 tests.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014LCQmFvKshyAJsE8C3B5ET

.gitignore

@@ -4,3 +4,5 @@ __pycache__
 .vercel
 .env*.local
 .DS_Store
+.venv/
+__pycache__/