docs: add CLAUDE.md with project architecture and commands

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: cunla

CLAUDE.md

@@ -0,0 +1,60 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+```bash
+pnpm start          # Dev server (ng serve)
+pnpm build          # Production build → www/
+pnpm run build:prod # Ionic prod build with service worker (outputs to www/browser)
+pnpm test           # Karma unit tests
+pnpm lint           # ESLint
+```
+
+Run a single test file by passing `--include` to karma or by modifying the test entry temporarily. There is no shorthand script for this.
+
+Deploy: `firebase deploy` (targets `www/browser/`)
+
+## Architecture
+
+**Stack**: Angular 21 + Ionic 8 + Firebase (PWA)
+
+### Routing & Modules
+All feature pages are lazy-loaded modules. Routes in `app-routing.module.ts`:
+- `''` → redirects to `today`
+- `today` / `day/:day` → `TodayPageModule` (main reading view)
+- `month/:month` → `MonthPageModule` (calendar view)
+- `notes` → `NotesPageModule`
+- `login` / `signup` → auth modules
+
+### Data Flow
+- **Reading content** (the actual Harvard Classics text) is static JSON loaded from `assets/index.json` via `MaterialService`. It is **not** in Firestore.
+- **User data** (completed days, favorites, notes) lives in Firestore at `/users/{userEmail}` and is subscribed to via `ReadingDbService` using RxJS `valueChanges()`.
+- **Auth state** is persisted in `localStorage` by `AuthService` (Firebase email/password + Google OAuth).
+
+### Inter-Component Communication
+A custom event bus (`Events` service, `services/events.service.ts`) uses a `Map`-based pub/sub pattern. Constants for event names are in `constants.ts`:
+- `EVENT_FINISHED_READING` — fired when scroll reaches 100% in TodayPage; consumed by `ReadingDbService` to mark the day read
+- `EVENT_USER_LOGIN` / `EVENT_USER_LOGOUT` — fired by AuthService
+
+### Key Services
+| Service | Responsibility |
+|---|---|
+| `ReadingDbService` | All Firestore reads/writes (days read, notes, favorites) |
+| `AuthService` | Firebase auth, localStorage session |
+| `MaterialService` | Loads/caches `assets/index.json` reading content |
+| `Events` | Pub/sub event bus between components |
+
+### TodayPage
+The main reading component. It:
+1. Loads content via `MaterialService`
+2. Tracks scroll progress — publishes `EVENT_FINISHED_READING` at 100%
+3. Uses `TextSelectEventDirective` to capture highlighted text for note creation
+4. Reads/writes notes and favorites to Firestore via `ReadingDbService`
+
+### Environments & Firebase
+Firebase config is in `src/environments/environment.ts` (dev) and `environment.prod.ts` (prod). Angular replaces the file at build time. The Firebase project is `harvardclassics365`.
+
+### PWA / Service Worker
+Service worker is only enabled in production builds (`build:prod`). Config is in `ngsw-config.json`. Versioned assets are cached long-term; `ngsw.json` itself is never cached (per `firebase.json` headers).