Fix PPI → PII terminology across entire codebase

All references to "PPI" (Personal Private Information) have been
corrected to the industry-standard "PII" (Personally Identifiable
Information). This includes UI labels, comments, CSS class comments,
and variable/function names (PPI_PATTERNS → PII_PATTERNS,
autoDetectPPI → autoDetectPII, scanInputForPPI → scanInputForPII,
ppiWarnings → piiWarnings).

Files changed: README.md, content.css, content.js, auto-detect.js,
org-policy.js, storage.js, options.html, popup.html, popup.js

https://claude.ai/code/session_01NNBEPuXMFGWezJb1f958nL

src/lib/storage.js

@@ -23,7 +23,7 @@ const KEYS = {
   SETTINGS: 'ss_settings',
 };
 
-// Keys that contain sensitive PPI and should be encrypted at rest
+// Keys that contain sensitive PII and should be encrypted at rest
 // All user data keys are encrypted at rest — settings included since
 // custom domains and configuration can reveal what services the user
 // accesses. Only ss_sync_encryption (salt, verification blob) and