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/lib/storage.js

@@ -20,6 +20,7 @@ const DEFAULT_SETTINGS = {
   revealMode: false,
   secretScanning: true,
   autoDetect: true,
+  autoAddDetected: true,
   maxLogEntries: 200,
   customDomains: [],
   categories: ['name', 'email', 'phone', 'address', 'ssn', 'dob', 'domain', 'general'],