feat: initial Silent Send browser extension

Chrome Manifest V3 extension that intercepts personal data and
substitutes it with user-defined replacements before sending to
Claude.ai. Hooks fetch() in the page's main world to catch API
requests, with bidirectional substitution (real→fake on send,
fake→real on display via reveal mode).

Includes popup UI with mapping management, live test/diff view,
activity log with badge count, options page with import/export,
and Shadow DOM traversal for Claude.ai compatibility.

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

icons/generate-icons.html

@@ -0,0 +1,2 @@
+<!-- Open this in a browser to generate PNG icons, or use the SVGs directly -->
+<!-- For development, we'll create simple SVG icons -->

icons/icon128.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="128" height="128" viewBox="0 0 128 128">
+  <rect width="128" height="128" rx="24" fill="#111"/>
+  <text x="64" y="82" font-family="Arial,sans-serif" font-size="56" font-weight="bold" fill="#10b981" text-anchor="middle">SS</text>
+</svg>

icons/icon16.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 128 128">
+  <rect width="128" height="128" rx="24" fill="#111"/>
+  <text x="64" y="82" font-family="Arial,sans-serif" font-size="56" font-weight="bold" fill="#10b981" text-anchor="middle">SS</text>
+</svg>

icons/icon48.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="48" height="48" viewBox="0 0 128 128">
+  <rect width="128" height="128" rx="24" fill="#111"/>
+  <text x="64" y="82" font-family="Arial,sans-serif" font-size="56" font-weight="bold" fill="#10b981" text-anchor="middle">SS</text>
+</svg>