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>

go.mod

@@ -0,0 +1,18 @@
+module git.wntrmute.dev/mc/mcdoc
+
+go 1.25.7
+
+require (
+	github.com/alecthomas/chroma/v2 v2.18.0
+	github.com/go-chi/chi/v5 v5.2.5
+	github.com/pelletier/go-toml/v2 v2.3.0
+	github.com/spf13/cobra v1.10.2
+	github.com/yuin/goldmark v1.7.12
+	github.com/yuin/goldmark-highlighting/v2 v2.0.0-20230729083705-37449abec8cc
+)
+
+require (
+	github.com/dlclark/regexp2 v1.11.5 // indirect
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+)