Resolve all open questions, remove /health from main listener (ADR-022)

Resolve OQ-08 through OQ-12 after reviewing implementation findings:

- OQ-08: Remove /health route from the main HTTPS listener entirely.
  Health checking belongs on port 9900 and admin socket only, not on
  the public-facing proxy. This eliminates upstream collision problems
  and special-case routing logic. (ADR-022)

- OQ-09: Not an architectural unknown — ADR-015 already decided on a
  separate connect timeout. The implementation gap is a known issue.

- OQ-10: Not an open question — acme_contact is already specified as
  required in config.md. The empty contact list is bug C2.

- OQ-11: Hardcoded is_https=true is correct for a TLS-terminating
  proxy. HTTP listener redirects, doesn't proxy. Just needs a comment.

- OQ-12: Access logging is already specified as mandatory/always-on in
  operations.md. Missing log_request! calls are bug W13.

Updated docs: proxy.md, operations.md, overview.md, config.md,
open-questions.md, README.md, ADR-013. Created ADR-022.

docs/architecture/decisions/022-health-check-scope.md

@@ -0,0 +1,56 @@
+# ADR-022: Health Check Scope — Local Port and Admin Socket Only
+
+## Status
+
+Accepted
+
+## Context
+
+The implementation served a `GET /health` route on the main HTTPS listener that
+returned 200 OK regardless of the Host header. This route was evaluated before
+host-based routing, meaning any upstream application using `/health` for its own
+health checks would have those requests silently intercepted by the proxy and
+never reach the upstream (implementation review finding W5).
+
+The architecture already specified a separate local health check port (9900,
+bound to 127.0.0.1 only) via ADR-013. The question was whether to keep the
+main-listener `/health` route alongside the dedicated port (and possibly make
+the path configurable), or to remove it entirely.
+
+## Decision
+
+The main HTTPS listener does **not** serve a `/health` route. Health checking is
+handled exclusively by:
+
+1. **Local health check port** (default: 9900, bound to `127.0.0.1`) — serves
+   `GET /health → 200 OK`. This is the primary health check mechanism for
+   container orchestration, load balancers, and monitoring systems.
+2. **Admin socket** (`status` command) — returns process information including
+   uptime and site count.
+
+The `/health` route is removed from the main listener entirely. No configurable
+path is needed because the route simply does not exist on the public listener.
+
+## Consequences
+
+**Positive:**
+- No collision with upstream applications that use `/health` for their own
+  health checks
+- The main listener's routing logic is simpler — all requests go through
+  host-based routing, no special cases
+- Clear separation of concerns: the main listener proxies, the local port
+  answers health checks
+- No configurable path needed — the problem disappears entirely
+
+**Negative:**
+- External monitoring that needs to verify TLS is working must connect to the
+  HTTPS port directly and check for a successful TLS handshake or a 404
+  response, rather than getting a 200 from `/health`. This is a minor
+  inconvenience — any successful TLS response (even 404) confirms the proxy is
+  serving TLS correctly.
+
+## References
+
+- ADR-013: Health check on separate local port
+- OQ-08: Resolved by this ADR
+- Implementation review finding W5 (hardcoded `/health` path)