feat: pre-send PPI detection — warns while typing, auto-add mappings

Like spellcheck for privacy. Scans text as you type and paste
into chat inputs (debounced 800ms). Shows a dark floating warning
panel listing detected PPI BEFORE you hit Enter.

Each detected item has a green [+] button that instantly:
1. Generates a plausible fake value (random IP, fake address, etc.)
2. Adds it as a mapping to storage
3. Shows a checkmark to confirm

The warning disappears when you clear the text or when all
detected items have been addressed.

Three new Options toggles:
- Auto-detect unconfigured PPI (on by default)
- Offer to auto-add detected PPI (on by default)

Also adds a storage bridge (postMessage) so the page-world
content script can read/write chrome.storage through the
injector.

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/content/injector.js

@@ -126,6 +126,24 @@
         }, '*');
       }
     });
+
+    // Storage bridge — lets page world script read/write storage
+    window.addEventListener('message', async (event) => {
+      if (event.source !== window) return;
+
+      if (event.data?.type === 'ss:storage-get') {
+        const result = await api.storage.local.get(event.data.key);
+        window.postMessage({
+          type: 'ss:storage-result',
+          id: event.data.id,
+          value: result[event.data.key] || null,
+        }, '*');
+      }
+
+      if (event.data?.type === 'ss:storage-set') {
+        await api.storage.local.set({ [event.data.key]: event.data.value });
+      }
+    });
   }
 
   init();