Decompose implementation review fixes into 14 atomic tasks with post-fix review

Break down findings from review #002 into dependency-ordered fix tasks:

Critical/High:
- fix/acme-contact-and-challenge (C1+C2): Add acme_contact field, wire to
  ACME, remove unused challenge_config, add validation rule 19
- fix/remove-health-and-hardcode-https (W5+W14+ADR-022): Remove /health
  from main listener, hardcode X-Forwarded-Proto to https
- fix/config-reload-static-drift (C4): Use ArcSwap<StaticConfig> so reload
  diffs against last config, not startup config
- fix/access-logging (W13): Wire up log_request! macro for every proxied
  request with client_ip, host, method, path, status, upstream, duration_ms

Medium:
- fix/graceful-shutdown (W1+W7): Join HTTPS tasks with timeout instead of
  abort, add shutdown signal to admin socket and eviction task
- fix/connect-timeout (W4): Wire upstream_connect_timeout_secs to enforce
  separate connect timeout

Low/Independent:
- fix/token-bucket-nanosecond (W6): Use as_nanos() instead of as_millis()
- fix/normalize-host-ipv6 (S3): Handle IPv6 bracket notation in normalize_host
- fix/http-port-validation (S1): Validate http_port in range 0 or 1-65535
- fix/integration-test-toml (S10): Fix double-nested listeners.listeners.sites
- fix/logging-test-global-subscriber (W9): Use try_init() to avoid test conflicts
- fix/fragile-error-detection (W3): Add typed error matching or documented string match
- fix/add-code-comments (C3,W8,W10,W11,S9): Document correct-but-non-obvious behaviors
- fix/request-timeout-scope (S8): Document full-request timeout scope
- fix/clean-dead-code (S4+S2): Remove dead_code annotations, add #[non_exhaustive]

Review gate:
- review/post-fix-review: Verify all fixes against architecture spec

tasks/fix/http-port-validation.md

@@ -0,0 +1,55 @@
+---
+id: fix/http-port-validation
+name: Add http_port range validation (0 or 1-65535)
+status: pending
+depends_on: []
+scope: single
+risk: trivial
+impact: isolated
+level: implementation
+review_findings: [S1]
+---
+
+## Description
+
+The `http_port` validation only checks for port conflicts and whether `http_port > 0` (for the conflict check). It doesn't validate that `http_port` is in the valid range: 0 (disabled) or 1-65535. A value like `65536` or `-1` would pass validation incorrectly. There's already a `HttpsPortInvalid` error for https_port, but no equivalent for http_port.
+
+### Changes Required
+
+**`src/config/validation.rs`**:
+- Add a validation check after the existing `http_port` conflict logic:
+  ```rust
+  if listener.http_port > 65535 {
+      errors.push(ValidationError::HttpPortInvalid {
+          bind_addr: listener.bind_addr.clone(),
+          http_port: listener.http_port,
+      });
+  }
+  ```
+- Note: `http_port = 0` is already treated as "disabled" and should be allowed, so only check `> 65535`
+
+**Tests**:
+- Add a test for `http_port = 65536` producing `HttpPortInvalid`
+- Add a test for `http_port = 0` still being valid (disabled)
+
+## Acceptance Criteria
+
+- [ ] `http_port > 65535` produces a validation error
+- [ ] `http_port = 0` (disabled) remains valid
+- [ ] `http_port` in 1-65535 remains valid
+- [ ] New `HttpPortInvalid` error variant with descriptive message
+- [ ] Existing validation tests pass
+- [ ] `cargo clippy` passes with no warnings
+
+## References
+
+- docs/reviews/002-implementation-review.md — S1 finding
+- src/config/validation.rs — existing validation logic
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion