feat. rebuild service in Go

Rebuild the Gitea Codex review bot from the product contract with a Go HTTP service, durable SQL queue, typed Gitea client, isolated runner, and deployment updates.

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

migrations/0001_initial.sql

@@ -0,0 +1,3 @@
+-- The Go migrator creates this logical schema with dialect-specific SQL.
+-- This file documents the compatibility baseline: webhook_events, review_jobs,
+-- review_runs, and bot_comments with the constraints described in README.md.

migrations/0002_trigger_comment_body.sql

@@ -0,0 +1 @@
+-- Compatibility migration: add review_jobs.trigger_comment_body when absent.