feat: auto-redact detected PPI on send + standard fake values

Detected PPI is now auto-redacted in the fetch hook using
RFC/standard reserved values — not just warned about:

- IPs → 192.0.2.1 (RFC 5737 TEST-NET-1, never routed)
- MACs → 00:00:00:00:00:00
- Addresses → 123 Example Street, Anytown, ST 00000
- GPS → 0.000000,0.000000 (Gulf of Guinea)
- Dates → 01/01/1970 (Unix epoch)
- EINs → 00-0000000 (impossible prefix)
- Paths → /home/user
- Git → example org

These are obviously fake and guaranteed not to be real data,
unlike random values which could be confused with actual PPI.

New Options toggle: "Auto-redact detected PPI on send" (on by
default). When on, PPI is caught in the fetch hook even if the
user hits Enter immediately after pasting. Warning banner now
says "Auto-redacted with standard placeholders" instead of
"These were sent as-is."

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/options/options.html

@@ -67,6 +67,16 @@
           <span class="toggle-slider"></span>
         </label>
       </div>
+      <div class="setting-row">
+        <div>
+          <label>Auto-redact detected PPI on send</label>
+          <p class="setting-desc">Automatically replace detected PPI with generic placeholders (192.0.2.1, 123 Example Street, etc.) when sending</p>
+        </div>
+        <label class="toggle">
+          <input type="checkbox" id="autoRedactDetected" checked>
+          <span class="toggle-slider"></span>
+        </label>
+      </div>
       <div class="setting-row">
         <div>
           <label>Offer to auto-add detected PPI</label>