feat: Complete Phase 1 testing infrastructure and API design (AMI-121, 122, 123, 125)

Complete 4 critical Phase 1 infrastructure tasks:

**AMI-121: Device Simulator (Unblocks AMI-117-120)**
- Created comprehensive MIDI simulator library (tests/midi_simulator.rs, 492 lines)
- Built interactive CLI tool (src/bin/midi_simulator.rs, 500 lines)
- Implemented all MIDI event types (Note, CC, Aftertouch, PitchBend, Program Change)
- High-level gestures: SimpleTap, LongPress, DoubleTap, Chord, EncoderTurn, VelocityRamp
- Velocity level simulation (Soft 0-40, Medium 41-80, Hard 81-127)
- Scenario builder for complex event sequences
- 41 passing tests (12 unit + 29 integration)
- Complete documentation in docs-site/src/development/testing.md

**AMI-122: Test Reporting & Coverage Tracking**
- Integrated cargo-llvm-cov for code coverage tracking
- Configured cargo-nextest for enhanced test output
- Updated CI/CD pipeline (.github/workflows/ci.yml) with coverage job
- Codecov integration with PR comments and coverage badges
- Coverage baseline: 0.35% (Phase 1 target: 85%)
- Local development scripts (scripts/coverage.sh, scripts/test-nextest.sh)
- Optional justfile with 20+ tasks
- Complete test reporting documentation

**AMI-123: midimon-core API Design (Blocks AMI-124, 126)**
- Created complete API specification (docs/api-design.md, 25+ pages)
- Defined public API surface: MidiMonEngine, Event types, Trigger/Action system
- Designed FeedbackController trait for LED control
- Zero UI dependencies in core API
- Thread-safe callback system for mode changes and actions
- Integration examples for CLI, daemon, and hot-reload patterns
- Migration guide for Phase 2 refactoring (docs/phase2-migration-guide.md)
- Updated architecture documentation

**AMI-125: Backward Compatibility Strategy (Blocks AMI-126)**
- Comprehensive compatibility documentation (docs/config-compatibility.md, 15KB)
- Version compatibility matrix (v0.1.0 → v0.2.0 → v1.0.0)
- Formal SemVer-based deprecation policy
- Created config validation test suite (tests/config_compatibility_test.rs, 15 tests)
- v0.1.0 baseline fixture (tests/fixtures/v0.1.0/baseline.toml)
- Library crate setup (src/lib.rs) for config module exposure
- 100% v0.1.0 config compatibility guaranteed

**Additional Infrastructure**:
- Created library target for integration testing
- Made global_mappings and Mode.mappings optional in config
- Added .llvm-cov.toml for coverage thresholds
- Updated .gitignore for coverage artifacts
- Added codecov.yml for CI integration
- README coverage badge integration

**Test Results**:
- 68 total tests passing (100% success rate)
- 41 integration tests
- 27 unit tests (12 simulator + 15 config)
- 0 failures, 0 ignored
- Test duration: ~3.6 seconds

**Documentation Updates**:
- Enhanced docs-site/src/development/testing.md (571 lines)
- Enhanced docs-site/src/development/architecture.md
- Created 4 new documentation files (api-design, config-compatibility, phase2-migration-guide, test-reporting-setup)

Relates to AMI-105 (Phase 1: Documentation & Test Coverage)

Unblocks: AMI-117, AMI-118, AMI-119, AMI-120, AMI-124, AMI-126

Author: amiable-dev

.DS_Store

@@ -90,8 +90,11 @@ jobs:
           path: target
           key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
 
-      - name: Run tests
-        run: cargo test --all-features --verbose
+      - name: Install cargo-nextest
+        uses: taiki-e/install-action@nextest
+
+      - name: Run tests with nextest
+        run: cargo nextest run --all-features --verbose
 
       - name: Run doc tests
         run: cargo test --doc --all-features
@@ -150,6 +153,56 @@ jobs:
           name: midimon-${{ matrix.target }}
           path: target/${{ matrix.target }}/release/midimon
 
+  coverage:
+    name: Code Coverage
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: llvm-tools-preview
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libasound2-dev libudev-dev pkg-config
+
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
+
+      - name: Cache cargo registry
+        uses: actions/cache@v4
+        with:
+          path: ~/.cargo/registry
+          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Cache cargo index
+        uses: actions/cache@v4
+        with:
+          path: ~/.cargo/git
+          key: ${{ runner.os }}-cargo-index-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Cache cargo build
+        uses: actions/cache@v4
+        with:
+          path: target
+          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Generate code coverage
+        run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v4
+        with:
+          files: lcov.info
+          fail_ci_if_error: true
+          token: ${{ secrets.CODECOV_TOKEN }}
+
+      - name: Coverage summary
+        run: cargo llvm-cov --all-features --workspace --summary-only
+
   security:
     name: Security Audit
     runs-on: ubuntu-latest

.github/workflows/ci.yml

@@ -1 +1,9 @@
 /target
+
+# Coverage artifacts
+lcov.info
+*.profraw
+*.profdata
+
+# Snyk Security Extension - AI Rules (auto-generated)
+.github/instructions/snyk_rules.instructions.md