docs: add CLAUDE.md project instructions

Co-Authored-By: Virgil <virgil@lethean.io>

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Documentation platform for the Core ecosystem (CLI, Go packages, PHP modules, MCP tools). Published at https://core.help. Two main components:
+
+1. **`docs/`** — Markdown source files (217+) with YAML frontmatter, organized by section (Go, PHP, TS, GUI, AI, Tools, Deploy, Publish)
+2. **`pkg/help/`** — Go library for help content management: parsing, search, HTTP serving, and static site generation
+
+## Common Commands
+
+```bash
+# Run all tests
+go test ./...
+
+# Run a single test
+go test ./pkg/help/ -run TestFunctionName
+
+# Run benchmarks
+go test ./pkg/help/ -bench .
+
+# Build the static documentation site (requires Python + zensical)
+pip install zensical
+zensical build
+```
+
+## Architecture: `pkg/help/`
+
+The Go help library is display-agnostic — it can serve HTML, expose a JSON API, or generate a static site from the same content.
+
+**Data flow:** Markdown files → `ParseTopic()` (parser.go) → `Topic` structs → `Catalog` (catalog.go) → consumed by Server, Search, or Generate.
+
+Key types and their roles:
+- **`Topic`/`Frontmatter`** (topic.go) — Data model. Topics have ID, title, content, sections, tags, related links, and sort order. Frontmatter is parsed from YAML `---` blocks.
+- **`Catalog`** (catalog.go) — Topic registry with `Add`, `Get`, `List`, `Search`. `LoadContentDir()` recursively loads `.md` files from a directory. `DefaultCatalog()` provides built-in starter topics.
+- **`searchIndex`** (search.go) — Full-text search with TF-IDF scoring, prefix matching, fuzzy matching, stemming (Porter stemmer in stemmer.go), and phrase detection. Title matches are boosted.
+- **`Server`** (server.go) — HTTP handler with HTML routes (`/`, `/topics/{id}`, `/search`) and JSON API routes (`/api/topics`, `/api/topics/{id}`, `/api/search`).
+- **`Generate*`** (generate.go) — Static site generator producing index, topic pages, 404, and `search-index.json` for client-side search.
+- **`Render*`/`Layout*`** (render.go, layout.go) — HTML rendering using `forge.lthn.ai/core/go-html` (HLCRF layout pattern with dark theme).
+- **`IngestHelp`** (ingest.go) — Converts Go CLI `--help` text output into structured `Topic` objects.
+
+## Site Configuration
+
+`zensical.toml` defines the doc site structure — navigation tree, theme settings, markdown extensions (admonition, mermaid, tabbed content, code highlighting). Zensical is a Python-based static site generator.
+
+## CI/CD
+
+Forgejo workflow (`.forgejo/workflows/deploy.yml`): on push to `main`, builds with `zensical build` and deploys the `site/` directory to BunnyCDN via s3cmd.
+
+## Conventions
+
+- License: EUPL-1.2 (SPDX headers in source files)
+- Go module: `forge.lthn.ai/core/docs`
+- Tests use `testify/assert` and `testify/require`
+- Markdown files use YAML frontmatter (`title`, `tags`, `related`, `order` fields)