Implement mcdoc v0.1.0: public documentation server

Single-binary Go server that fetches markdown from Gitea (mc org),
renders to HTML with goldmark (GFM, chroma syntax highlighting,
heading anchors), and serves a navigable read-only documentation site.

Features:
- Boot fetch with retry, webhook refresh, 15-minute poll fallback
- In-memory cache with atomic per-repo swap
- chi router with htmx partial responses for SPA-like navigation
- HMAC-SHA256 webhook validation
- Responsive CSS, TOC generation, priority doc ordering
- $PORT env var support for MCP agent port assignment

33 tests across config, cache, render, and server packages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

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+FROM golang:1.25-alpine AS builder
+
+ARG VERSION=dev
+
+RUN apk add --no-cache git
+
+WORKDIR /build
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+RUN CGO_ENABLED=0 go build -trimpath -ldflags="-s -w -X main.version=${VERSION}" -o mcdoc ./cmd/mcdoc
+
+FROM alpine:3.21
+
+RUN apk add --no-cache ca-certificates tzdata
+
+COPY --from=builder /build/mcdoc /usr/local/bin/mcdoc
+
+WORKDIR /srv/mcdoc
+EXPOSE 8080
+
+ENTRYPOINT ["mcdoc"]
+CMD ["server", "--config", "/srv/mcdoc/mcdoc.toml"]