fix: add dist-check guard + List<T> type parsing + state machine examples

- check-dist.sh: Prevents DIST DESYNC by verifying all dist/*.js files
  are newer than their src/*.ts sources. Fails build if stale.
- Makefile: Standard build targets (build/check-dist/test/recompile/clean)
- src/index.ts: Integrated dist freshness check before compilation
- src/parser.ts: Added List<T> type parsing alongside existing Set<T>/Map<K,V>
  (e.g., 'log: List<LogEntry>' now parses as { type: 'list', elementType })
- examples/: Restored v0.3 state machine specs (TigerBeetleLedger,
  AccountLedger, ToggleSwitch, TwoPhaseCommit)
- DIST DESYNC is a known recurring anti-pattern — this guard prevents it

Tests: 39/41 pass (2 pre-existing E2E WASM failures due to missing wabt)

examples/ToggleSwitch.speck

@@ -0,0 +1,30 @@
+speck ToggleSwitch {
+    // Simplest possible state machine: on/off toggle
+    // Demonstrates the v0.3 imperative action body syntax
+
+    state {
+        isOn: Bool
+    }
+
+    init {
+        isOn == false
+    }
+
+    invariant SwitchConsistent {
+        isOn in {true, false}
+    }
+
+    action TurnOn {
+        require not isOn
+        isOn := true
+        return isOn
+    }
+
+    action TurnOff {
+        require isOn
+        isOn := false
+        return isOn
+    }
+
+    next: TurnOn | TurnOff
+}