feat(clarity-assist): add vagueness detection hook (#227)

Implements UserPromptSubmit hook to detect vague prompts:
- Checks for short prompts without context
- Detects ambiguous phrases ("fix it", "help me with")
- Suggests /clarity-assist when beneficial
- Non-blocking, configurable via CLARITY_ASSIST_AUTO_SUGGEST

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/clarity-assist/hooks/hooks.json

@@ -0,0 +1,10 @@
+{
+  "hooks": {
+    "UserPromptSubmit": [
+      {
+        "type": "command",
+        "command": "${CLAUDE_PLUGIN_ROOT}/hooks/vagueness-check.sh"
+      }
+    ]
+  }
+}