feat: auto-detect unconfigured PPI — warns before sending

Scans outbound messages AFTER all substitutions for personal data
the user forgot to configure:

- Private/public IP addresses (skips 127.0.0.1, 8.8.8.8, etc.)
- MAC addresses
- Street addresses ("123 Main St")
- GPS coordinates
- Dates (possible DOBs)
- EIN/tax IDs
- Home directory paths not caught by smart patterns
- Shell prompts (user@host)
- Git remotes (reveals username/org)
- Environment variable assignments (HOME=, USER=, etc.)

Shows a floating dark warning banner (top-right, auto-dismisses
after 15s) listing each detected item with its type, value, and
hint. Skips values already in the user's identity config.

Also shows PPI warnings in the popup Test tab and adds toggle
in Options to disable auto-detect.

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/lib/storage.js

@@ -19,6 +19,7 @@ const DEFAULT_SETTINGS = {
   showHighlights: false,
   revealMode: false,
   secretScanning: true,
+  autoDetect: true,
   maxLogEntries: 200,
   customDomains: [],
   categories: ['name', 'email', 'phone', 'address', 'ssn', 'dob', 'domain', 'general'],