feat: add reveal paste-back tool + fix smart detection bail

Test tab now has two modes:
- Strip (real → fake): paste text with real data, see what gets sent
- Reveal (fake → real): paste AI output with fake data, get back
  real data with a "Copy to Clipboard" button

Also fixes:
- content.js smartSubstitute bailing when identity.enabled was
  undefined (defaulted enabled to all-true instead of returning)
- Test tab now reloads identity from storage on tab switch so
  changes saved in the Identity tab take effect immediately
- Shows yellow warning when identity fields are missing

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/content/content.js

@@ -95,7 +95,9 @@
   ]);
 
   function smartSubstitute(text, id) {
-    if (!id || !id.enabled) return { text, replacements: [] };
+    if (!id) return { text, replacements: [] };
+    // Default enabled to all-true if not set
+    if (!id.enabled) id.enabled = { emails: true, names: true, usernames: true, phones: true, paths: true };
     const replacements = [];
     let result = text;