feat: Harbour-compatible VM shutdown sequence

Implements full cleanup on program exit (normal, Ctrl+C, crash):
- EXIT PROCEDURE auto-execution (reverse module order)
- AtExit callback registry (LIFO order)
- All WorkAreas auto-close (child before parent)
- Terminal restore (raw → normal) on signal/exit
- Static variables clear
- Signal handlers (SIGINT, SIGTERM) for clean shutdown
- shutdown.go: Harbour hb_vmQuit() 25-step sequence adapted for Five
- vm.go: Run() now calls Shutdown() via defer
- rawtty.go: terminal restore registered with shutdown system

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/.pdca-status.json

@@ -1,6 +1,6 @@
 {
   "version": "2.0",
-  "lastUpdated": "2026-03-30T23:17:34.469Z",
+  "lastUpdated": "2026-03-31T01:06:49.182Z",
   "activeFeatures": [
     "hbrt",
     "hbrtl",
@@ -32,9 +32,9 @@
       "documents": {},
       "timestamps": {
         "started": "2026-03-27T09:33:04.512Z",
-        "lastUpdated": "2026-03-30T23:17:34.469Z"
+        "lastUpdated": "2026-03-31T01:05:45.128Z"
       },
-      "lastFile": "/mnt/d/charles/five/hbrt/macroeval_test.go"
+      "lastFile": "/mnt/d/charles/five/hbrt/vm.go"
     },
     "hbrtl": {
       "phase": "do",
@@ -45,9 +45,9 @@
       "documents": {},
       "timestamps": {
         "started": "2026-03-27T11:15:10.675Z",
-        "lastUpdated": "2026-03-29T13:02:52.259Z"
+        "lastUpdated": "2026-03-31T01:06:49.182Z"
       },
-      "lastFile": "/mnt/d/charles/five/hbrtl/json_test.go"
+      "lastFile": "/mnt/d/charles/five/hbrtl/rawtty.go"
     },
     "tests": {
       "phase": "do",
@@ -266,7 +266,7 @@
   "session": {
     "startedAt": "2026-03-27T06:06:49.620Z",
     "onboardingCompleted": false,
-    "lastActivity": "2026-03-30T23:17:34.469Z"
+    "lastActivity": "2026-03-31T01:06:49.182Z"
   },
   "history": [
     {
@@ -5290,6 +5290,42 @@
       "feature": "hbrt",
       "phase": "do",
       "action": "updated"
+    },
+    {
+      "timestamp": "2026-03-31T01:04:07.876Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-03-31T01:04:54.144Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-03-31T01:05:27.088Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-03-31T01:05:45.128Z",
+      "feature": "hbrt",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-03-31T01:06:16.666Z",
+      "feature": "hbrtl",
+      "phase": "do",
+      "action": "updated"
+    },
+    {
+      "timestamp": "2026-03-31T01:06:49.182Z",
+      "feature": "hbrtl",
+      "phase": "do",
+      "action": "updated"
     }
   ]
 }