Add architecture document and project guidelines

Detailed architecture covering Tauri + Svelte frontend, Rust backend,
Python sidecar for ML (faster-whisper, pyannote.audio), IPC protocol,
SQLite schema, AI provider system, export formats, and phased
implementation plan with agent work breakdown.

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

CLAUDE.md

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+# Voice to Notes — Project Guidelines
+
+## Project Overview
+Desktop app for transcribing audio/video with speaker identification. Runs locally on user's computer. See `docs/ARCHITECTURE.md` for full architecture.
+
+## Tech Stack
+- **Desktop shell:** Tauri v2 (Rust backend + Svelte/TypeScript frontend)
+- **ML pipeline:** Python sidecar process (faster-whisper, pyannote.audio, wav2vec2)
+- **Database:** SQLite (via rusqlite in Rust)
+- **AI providers:** LiteLLM, OpenAI, Anthropic, Ollama (local)
+- **Caption export:** pysubs2 (Python)
+- **Audio UI:** wavesurfer.js
+- **Transcript editor:** TipTap (ProseMirror)
+
+## Key Architecture Decisions
+- Python sidecar communicates with Rust via JSON-line IPC (stdin/stdout)
+- All ML models must work on CPU. GPU (CUDA) is optional acceleration.
+- AI cloud providers are optional. Local models (Ollama) are a first-class option.
+- SQLite database is per-project, stored alongside media files.
+- Word-level timestamps are required for click-to-seek playback sync.
+
+## Directory Structure
+```
+src/                    # Svelte frontend source
+src-tauri/              # Rust backend source
+python/                 # Python sidecar source
+  voice_to_notes/       # Python package
+  tests/                # Python tests
+docs/                   # Architecture and design documents
+```
+
+## Conventions
+- Rust: follow standard Rust conventions, use `cargo fmt` and `cargo clippy`
+- Python: Python 3.11+, use type hints, follow PEP 8, use `ruff` for linting
+- TypeScript: strict mode, prefer Svelte stores for state management
+- IPC messages: JSON-line format, each message has `id`, `type`, `payload` fields
+- Database: UUIDs as primary keys (TEXT type in SQLite)
+- All timestamps in milliseconds (integer) relative to media file start
+
+## Platform Targets
+- Linux (primary development target)
+- Windows (must work, tested before release)
+- macOS (future, not yet targeted)