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>

Dockerfile

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+# syntax=docker/dockerfile:1
+
+# --- build: compile a static binary ----------------------------------------
+FROM golang:1.26 AS build
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 go build -o /out/gitmanager ./cmd/server
+
+# --- dev: hot reload with air (used by docker-compose) ---------------------
+FROM golang:1.26 AS dev
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends git ca-certificates openssh-client \
+ && rm -rf /var/lib/apt/lists/*
+RUN go install github.com/air-verse/air@latest
+WORKDIR /app
+EXPOSE 8080
+CMD ["air", "-c", ".air.toml"]
+
+# --- runtime: small image with git available -------------------------------
+# git is required at runtime — the app shells out to it for every Git operation
+# (AGENT.md §2). openssh-client + ca-certificates let it reach remotes.
+FROM debian:stable-slim AS runtime
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends git ca-certificates openssh-client \
+ && rm -rf /var/lib/apt/lists/*
+WORKDIR /app
+COPY --from=build /out/gitmanager /usr/local/bin/gitmanager
+COPY web ./web
+COPY components ./components
+EXPOSE 8080
+CMD ["gitmanager"]