Server: no built-in public host, no trusted proxy by default; OpenAPI server variable host (D-123)

KVITT_PUBLIC_URL is required: every command refuses to start without it (compose
always sets it). KVITT_TRUSTED_PROXY defaults to none, which the rate limiter never
resolves. contracts/openapi.yaml and the utoipa document: servers[].url
https://{host}:8443 with variable host (default kvitt.example.invalid). E-7 and E-12
examples on kvitt.example.invalid.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

contracts/openapi.yaml

@@ -23,7 +23,11 @@ info:
       `protocol_unsupported`, `rate_limited`, `internal`, `unavailable`; unauthenticated ones `rate_limited`,
       `internal`, `unavailable`. `not_implemented` (501) exists only during milestones M2a to M4.
 servers:
-  - url: https://icehack.asuscomm.com:8443
+  - url: https://{host}:8443
+    variables:
+      host:
+        default: kvitt.example.invalid
+        description: the owner-chosen Kvitt host name, SPEC §10.5
 security:
   - device: []