Add batch commands to PortTracker CLI and migrate batch tables into porting.db

Implements batch list/show/ready/next/start/complete commands with dependency
validation, migrates 42 implementation batches (2377 features, 2087 tests) from
porting_batches.db into the live tracking database, and documents the batch
workflow in AGENTS.md.

porting-schema.sql

@@ -99,6 +99,31 @@ CREATE TABLE IF NOT EXISTS status_overrides (
     created_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 
+CREATE TABLE IF NOT EXISTS implementation_batches (
+    id INTEGER PRIMARY KEY,
+    name TEXT NOT NULL,
+    description TEXT,
+    priority INTEGER NOT NULL,
+    feature_count INTEGER DEFAULT 0,
+    test_count INTEGER DEFAULT 0,
+    status TEXT DEFAULT 'pending',
+    depends_on TEXT,
+    go_files TEXT,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE IF NOT EXISTS batch_features (
+    batch_id INTEGER NOT NULL REFERENCES implementation_batches(id),
+    feature_id INTEGER NOT NULL REFERENCES features(id),
+    PRIMARY KEY (batch_id, feature_id)
+);
+
+CREATE TABLE IF NOT EXISTS batch_tests (
+    batch_id INTEGER NOT NULL REFERENCES implementation_batches(id),
+    test_id INTEGER NOT NULL REFERENCES unit_tests(id),
+    PRIMARY KEY (batch_id, test_id)
+);
+
 -- Indexes
 CREATE INDEX IF NOT EXISTS idx_features_module ON features(module_id);
 CREATE INDEX IF NOT EXISTS idx_features_status ON features(status);
@@ -109,6 +134,10 @@ CREATE INDEX IF NOT EXISTS idx_deps_source ON dependencies(source_type, source_i
 CREATE INDEX IF NOT EXISTS idx_deps_target ON dependencies(target_type, target_id);
 CREATE INDEX IF NOT EXISTS idx_library_status ON library_mappings(status);
 CREATE INDEX IF NOT EXISTS idx_modules_status ON modules(status);
+CREATE INDEX IF NOT EXISTS idx_batch_features_feature ON batch_features(feature_id);
+CREATE INDEX IF NOT EXISTS idx_batch_tests_test ON batch_tests(test_id);
+CREATE INDEX IF NOT EXISTS idx_batches_status ON implementation_batches(status);
+CREATE INDEX IF NOT EXISTS idx_batches_priority ON implementation_batches(priority);
 
 -- Triggers to auto-update updated_at
 CREATE TRIGGER IF NOT EXISTS trg_modules_updated AFTER UPDATE ON modules