sprint-0: foundations -- data model, seed library, tests, demo

Initial commit. Delivers what the brief calls 'Sprint 0 - Foundations'
(see docs/AR_Autopilot_brief.md section 12):

- Complete repository structure (arautopilot package + firmware, display,
  installer, tools placeholders + docs).
- Core data model (Pydantic v2): modes, alarms, actuator config, PID
  config + gain scheduling, vessel config, knob state machine, project
  config with YAML/JSON serialisation.
- Seed library: 2 actuator profiles (hydraulic & electric DC reversible)
  and 2 default tunings (yacht motor planeo 30 m and 40 m). Conservative
  literature values, NOT the integrator's production tuning IP.
- Firmware skeleton: only src/hal/pinout.h with the 21 I/O contract for
  the AR-NMEA-IO v1.0 board. No drivers, no main loop.
- Studio stubs (real PySide6 app starts in Sprint 4).
- pytest suite (80 tests, all green): modes, alarms, actuator, PID
  (incl. gain interpolation and the +/-50% adaptive bound from brief
  section 6), vessel, knob state, project config, library loader,
  end-to-end roundtrip.
- examples/sprint0_demo.py - the acceptance demo from the brief.

Acceptance criteria met:
- pytest green (80/80)
- demo creates, saves (YAML + JSON), reloads, and verifies a full
  ProjectConfig using the seed library
- repository ready for tag `sprint-0-approved`

See CHANGELOG.md for the detailed scope.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,139 @@
+# ============================================================================
+# AR-Autopilot — .gitignore
+# ============================================================================
+
+# ----------------------------------------------------------------------------
+# Python
+# ----------------------------------------------------------------------------
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# Virtual environments
+.venv/
+venv/
+env/
+ENV/
+.env
+
+# pytest / coverage / mypy / ruff
+.pytest_cache/
+.coverage
+.coverage.*
+htmlcov/
+.tox/
+.nox/
+coverage.xml
+*.cover
+.hypothesis/
+.mypy_cache/
+.dmypy.json
+dmypy.json
+.ruff_cache/
+
+# Jupyter
+.ipynb_checkpoints/
+
+# ----------------------------------------------------------------------------
+# Flutter / Dart (display app)
+# ----------------------------------------------------------------------------
+display/.dart_tool/
+display/.flutter-plugins
+display/.flutter-plugins-dependencies
+display/.packages
+display/.pub-cache/
+display/.pub/
+display/build/
+display/**/build/
+display/**/.dart_tool/
+display/**/.idea/
+display/**/*.iml
+display/ios/Pods/
+display/ios/.symlinks/
+display/android/.gradle/
+display/android/local.properties
+display/android/captures/
+display/android/gradlew
+display/android/gradlew.bat
+display/android/gradle-wrapper.jar
+display/windows/flutter/ephemeral/
+display/linux/flutter/ephemeral/
+display/macos/Flutter/ephemeral/
+
+# ----------------------------------------------------------------------------
+# PlatformIO / ESP32 firmware
+# ----------------------------------------------------------------------------
+firmware/**/.pio/
+firmware/**/.pioenvs/
+firmware/**/.piolibdeps/
+firmware/**/.vscode/
+firmware/**/.clang_complete
+firmware/**/.gcc-flags.json
+
+# ----------------------------------------------------------------------------
+# IDEs / Editors
+# ----------------------------------------------------------------------------
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.project
+.pydevproject
+.settings/
+
+# ----------------------------------------------------------------------------
+# OS files
+# ----------------------------------------------------------------------------
+.DS_Store
+Thumbs.db
+Desktop.ini
+*.lnk
+
+# ----------------------------------------------------------------------------
+# Build artifacts / installers
+# ----------------------------------------------------------------------------
+installer/output/
+installer/build/
+*.msi
+*.exe
+*.appack
+
+# ----------------------------------------------------------------------------
+# Local config / secrets
+# ----------------------------------------------------------------------------
+*.local.yaml
+*.local.json
+secrets/
+.env.local
+.secrets/
+
+# ----------------------------------------------------------------------------
+# Examples output
+# ----------------------------------------------------------------------------
+examples/output/
+
+# ----------------------------------------------------------------------------
+# Logs
+# ----------------------------------------------------------------------------
+*.log
+logs/