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>

CHANGELOG.md

@@ -0,0 +1,21 @@
+# Changelog
+
+Append-only running history of all changes (AGENT.md §9.1). Newest last.
+
+## 2026-09-19 — Project scaffold
+- **What:** Initial runnable skeleton for the GitManager multi-repo dashboard.
+  Added the Go backend (`cmd/server/main.go` + `internal/{config,logging,git,repos,render}`),
+  the Echo HTTP server with `/`, `/help`, `/healthz`, and `/api/repos`, a
+  read-only repo scanner that discovers repositories under `GIT_REPO_ROOTS` and
+  keeps an in-memory index, the `<repo-list>` web component, shared design tokens
+  (`web/static/app.css`), page shells (`web/templates/{index,help}.html`), and the
+  dev tooling: `Dockerfile` (build/dev/runtime stages), `docker-compose.yml`,
+  `.air.toml`, `.env.example`, `.gitignore`, `go.mod`.
+- **Why:** Stand up the architecture defined in AGENT.md so feature work can begin.
+- **Affects:** whole repo (foundation); `components/repo-list`.
+
+### Notes to confirm (from AGENT.md §11)
+- **Go module path** is the placeholder `gitmanager`; change it if this gets a
+  canonical import path (e.g. a GitHub URL).
+- All items in AGENT.md §11 (discovery strategy, background fetch, forge
+  providers, listen address, container credentials) remain open.