Add service layer and MCP server with read tools

Slice 1: internal/service is the one capability layer both the HTTP API and the MCP server call (AGENT.md 1.7); /api/repos and /api/repo route through it. Slice 2: internal/mcp serves an MCP server over Streamable HTTP at /mcp (go-sdk v1.8.0) with read tools list_repos and get_repo as thin adapters over the service, plus a round-trip test. Enabled air polling so hot reload works across the Docker-on-Windows bind mount.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -52,3 +52,20 @@ Append-only running history of all changes (AGENT.md §9.1). Newest last.
   stop cluttering repos. Decisions locked: cooperative pull-first handoff; Gitea
   writes enabled (confirmed per §1.4); MCP over HTTP `/mcp`.
 - **Affects:** `AGENT.md`, `.env.example` (architecture/contract only — no code).
+
+## 2026-09-19 — Service layer + MCP server (Claude integration, read tools)
+- **What:** Slice 1 — extracted `internal/service`, the one capability layer both
+  the HTTP API and the MCP server call (§1.7); the `/api/repos` and `/api/repo`
+  handlers now route through it. Slice 2 — added `internal/mcp`: an MCP server
+  (`github.com/modelcontextprotocol/go-sdk` v1.8.0) served over Streamable HTTP at
+  `/mcp`, with read tools `list_repos` and `get_repo` as thin adapters over the
+  service. Added a round-trip test (`internal/mcp/mcp_test.go`) using a real temp
+  git repo + the in-memory MCP transport. Verified the HTTP `/mcp` handshake
+  locally and in Docker.
+- **Why:** First step of the two-way Claude integration (AGENT.md §8.1) — prove
+  Claude can connect to the app over MCP before building deeper features on it.
+- **Affects:** `internal/service` (new), `internal/mcp` (new), `cmd/server/main.go`,
+  `go.mod`/`go.sum`, `.air.toml`.
+- **Gotcha:** Docker-on-Windows bind mounts do NOT deliver filesystem events, so
+  air's watch-based reload silently never fired. Fixed by enabling air polling
+  (`poll = true`, `poll_interval = 500` in `.air.toml`).