fix: remove broken Stop hook from doc-guardian

The Stop hook referenced a non-existent "internal queue" for tracking
documentation drift. Each hook runs in isolation with no way to pass
data between invocations, so the queue concept couldn't work.

The hook was causing errors on every session end:
"Stop hook error: Prompt hook condition was not met..."

Changes:
- Removed the Stop hook entirely
- Updated PostToolUse hook to report drift immediately when found
  (instead of referencing non-existent queue)

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

plugins/doc-guardian/hooks/hooks.json

@@ -6,18 +6,7 @@
         "hooks": [
           {
             "type": "prompt",
-            "prompt": "A file was just modified. Silently check if this change affects any documentation:\n\n1. If a code file changed: check if README, CLAUDE.md, docstrings, or API docs reference the modified functions/classes/configs\n2. If drift detected: add to internal queue (do NOT interrupt user flow)\n3. At natural breakpoints or when user runs /doc-sync: report pending doc updates\n\nDo NOT announce this check unless drift is found. Work silently."
+            "prompt": "A file was just modified. Silently check if this change affects any documentation:\n\n1. If a code file changed: check if README, CLAUDE.md, docstrings, or API docs reference the modified functions/classes/configs\n2. If drift detected: briefly mention it to the user (e.g., 'Note: This change may require updating X documentation')\n3. Do NOT block the workflow - just inform\n\nDo NOT announce this check unless drift is found. Work silently."
-          }
-        ]
-      }
-    ],
-    "Stop": [
-      {
-        "matcher": ".*",
-        "hooks": [
-          {
-            "type": "prompt",
-            "prompt": "Before ending, check if there are pending documentation updates queued by doc-guardian. If yes, ask user: 'I detected documentation drift in X files. Run /doc-sync to update, or skip for now?'"
           }
         ]
       }