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>

CLAUDE.md

@@ -34,7 +34,7 @@ go test ./internal/server -run TestDocPage
 ## Tech Stack
 
 - **Language:** Go 1.25+, `CGO_ENABLED=0`, statically linked
-- **Module path:** `git.wntrmute.dev/kyle/mcdoc`
+- **Module path:** `git.wntrmute.dev/mc/mcdoc`
 - **Config:** TOML via `go-toml/v2`, env overrides via `MCDOC_*`
 - **HTTP:** chi router, htmx for navigation
 - **Rendering:** goldmark (GFM), chroma (syntax highlighting)