Add CLAUDE.md for Claude Code guidance (#74)

Author: alexwolson

CLAUDE.md

@@ -0,0 +1,81 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is the [civictech.ca](https://civictech.ca) website — a Jekyll 4 static site for Civic Tech Toronto, hosted on GitHub Pages.
+
+## Development Commands
+
+```bash
+# Install Ruby dependencies
+make install          # or: bundle install
+
+# Start development server
+make serve            # http://localhost:4000
+make serve-incremental  # faster rebuilds
+
+# Regenerate tag/category data and pages (required after content changes)
+make generate
+
+# Update archives submodule to latest
+make update           # or: git submodule update --remote --merge
+
+# Clean build artifacts
+make clean
+```
+
+The `make generate` step must be run before serving if you've changed content in the `archives/` submodule, as it runs four shell scripts that extract tags and categories from front matter and write them to `_data/` and `tags/`/`categories/` directories.
+
+## Architecture
+
+### Content Lives in a Git Submodule
+
+All actual content (meetups, projects, people, organizations, venues, resources) lives in the `archives/` submodule — a separate repository updated daily by CI. The main repo contains only templates, styles, scripts, and site configuration. When working with content, always remember to initialize submodules:
+
+```bash
+git submodule update --init --recursive
+```
+
+### Jekyll Collections
+
+Defined in `_config.yml`, collections map to these URL paths:
+- `archives/_meetups/` → `/events/`
+- `archives/_projects/` → `/projects/`
+- `archives/_people/` → `/people/`
+- `archives/_organizations/` → `/organizations/`
+- `archives/_venues/` → `/venues/`
+- `archives/_resources/` → `/resources/`
+- `_announcements/` → `/announcements/`
+
+### Data Generation Pipeline
+
+Tags and categories are not manually maintained — they're generated from collection front matter by bash scripts in `_scripts/`:
+
+1. `generate_tag_data.sh` → writes `_data/tags.yml`
+2. `generate_tag_pages.sh` → writes `tags/*.html`
+3. `generate_category_data.sh` → writes `_data/categories.yml`
+4. `generate_category_pages.sh` → writes `categories/*.html`
+
+The CI build (`.github/workflows/pages.yml`) always runs `make generate` before `jekyll build`. Do not manually edit files in `tags/`, `categories/`, or `_data/tags.yml`/`_data/categories.yml` — they will be overwritten.
+
+### Navigation and Site Data
+
+Site-wide data is in `_data/`:
+- `navigation.yml` — header/footer nav structure
+- `footer_social.yml` — social links with `rel` attribute support (used for Mastodon verification)
+- `featured_topics.yml` — homepage featured topics
+
+### Image Handling
+
+The `jekyll_picture_tag` plugin processes images from `archives/images/` and caches generated thumbnails in `assets/thumbs/`. This requires `libvips` and `imagemagick` to be installed locally. The `assets/thumbs/` directory is gitignored and regenerated at build time.
+
+## CI/CD
+
+- **`pages.yml`**: Triggers on push to `main`. Runs `make generate`, then `jekyll build`, then deploys to GitHub Pages.
+- **`update-submodule.yml`**: Runs daily at midnight UTC, creates a PR to bump the `archives` submodule to its latest master commit.
+
+## Ruby Version
+
+The project requires Ruby 3.2.2 (specified in `.ruby-version`). Use `rbenv` or `rvm` to manage this.