fix: reveal pairs oscillating between populated and empty

Two bugs found:
1. Individual name parts ("Ademo"→"John", "Demo"→"Smith") were added
   as reveal pairs, causing partial replacements that corrupted the DOM.
   The smart engine sends combined forms ("Ademo Demo"→"John Smith")
   which the catch-all already handles. Removed individual name entries
   from buildRevealPairs — only emails, usernames, hostnames, phones
   are matched individually.

2. Cache invalidated on every ss:config-updated (including settings-only
   changes like reveal toggle). Now only invalidates when mappings or
   identity actually change.

https://claude.ai/code/session_01KF4i7Ra7zCEDskxDBaNtcT

manifest.firefox.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "Silent Send",
-  "version": "0.9.13",
+  "version": "0.9.14",
   "description": "Intercepts personal info and substitutes it with user-defined replacements before sending to AI services.",
   "browser_specific_settings": {
     "gecko": {