docs: rewrite developer-guide as architectural reference

- Remove implementation details that will rot (code templates, tutorials)
- Keep only stable contracts: ownership, lifecycle, protocols, error semantics
- 270 lines → reference that only changes when architecture changes

docs/getting-started.md

@@ -0,0 +1,68 @@
+# Getting Started
+
+Quickstart for developers working on Abogen.
+
+## Prerequisites
+
+- Python 3.10+
+- Node.js 20+
+- npm 10+
+- Git
+- Docker (optional)
+
+## Installation
+
+```bash
+# Development install with all extras
+pip install -e .[dev]
+
+# Or with uv
+uv pip install -e .[dev]
+```
+
+## Running the Application
+
+```bash
+# Desktop GUI
+abogen
+
+# Web UI
+abogen-web
+
+# CLI
+abogen-cli
+```
+
+## Project Structure
+
+```
+abogen/
+├── pyqt/         - PyQt6 desktop GUI
+├── webui/        - Flask web UI
+├── tts_plugin/   - Plugin Architecture (Engine, EngineSession, Manifest)
+└── plugins/      - Built-in plugins (kokoro, supertonic)
+tests/
+├── contracts/    - Contract compliance tests
+└── ...
+```
+
+## Testing
+
+```bash
+# All tests
+pytest
+
+# Contract tests (architectural compliance)
+pytest tests/contracts/
+
+# Behavioral regression tests
+pytest tests/test_behavioral_regression.py
+```
+
+## Architecture
+
+See [Developer Guide](developer-guide.md) for Plugin Architecture details:
+- Engine / EngineSession lifecycle
+- Plugin contract (PLUGIN_MANIFEST, create_engine)
+- Adding new plugins
+- Capability interfaces