Scaffold GitManager multi-repo dashboard

Runnable skeleton per AGENT.md: Echo server (/, /help, /healthz, /api/repos), read-only repo scanner with in-memory index, the internal/git boundary, the <repo-list> web component with design tokens, and dev tooling (Dockerfile, docker-compose, air, .env.example).

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

docker-compose.yml

@@ -0,0 +1,38 @@
+# Dev environment: `docker compose up` builds the app with hot reload (air) and
+# mounts your host repositories in (AGENT.md §1.6). Because the app operates on
+# repos that live on the host, the roots are mounted read-write.
+
+services:
+  app:
+    build:
+      context: .
+      target: dev
+    env_file: .env
+    environment:
+      # Bind all interfaces INSIDE the container so the published port reaches
+      # it; the `ports` mapping below still keeps it localhost-only on the HOST.
+      - LISTEN_ADDR=0.0.0.0:8080
+      # The scanner looks here; matches the volume mount below.
+      - GIT_REPO_ROOTS=/repos
+    ports:
+      - "127.0.0.1:8080:8080"
+    volumes:
+      # Source, for hot reload.
+      - .:/app
+      # Cache the Go module + build cache across restarts.
+      - gomod:/go/pkg/mod
+      # Your repositories. Set REPOS_HOST_PATH in .env (or your shell) to the
+      # host folder that holds them; defaults to ./repos next to this file.
+      - "${REPOS_HOST_PATH:-./repos}:/repos"
+      # --- Optional: let git authenticate to remotes from inside the container.
+      # Uncomment ONE approach and adjust for your host (AGENT.md §1.6, §11):
+      #   SSH agent socket (Linux/macOS):
+      # - "${SSH_AUTH_SOCK}:/ssh-agent"
+      #   or mounted keys (read-only):
+      # - "${HOME}/.ssh:/root/.ssh:ro"
+    # environment for the SSH-agent option:
+    # environment:
+    #   - SSH_AUTH_SOCK=/ssh-agent
+
+volumes:
+  gomod: