fix: activity log now records from injector + dynamic icon colors

Activity log fix:
- Injector now writes directly to storage.local in addition to
  sending runtime messages to the background worker. This fixes
  the issue where MV3 service worker sleep caused messages to be
  silently dropped.

Dynamic icon colors:
- Black "SS" = active, normal
- Blue "SS" = reveal mode on
- Red "SS" = Silent Send disabled
- Icons generated via OffscreenCanvas in the service worker
- Updates on every settings change and keyboard shortcut toggle

Also adds keyboard shortcuts section to Options page showing
current bindings and how to customize them per browser.

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/options/options.html

@@ -12,6 +12,29 @@
       <p class="subtitle">Manage your privacy substitution mappings</p>
     </header>
 
+    <section class="section">
+      <h2>Keyboard Shortcuts</h2>
+      <div class="setting-row">
+        <div>
+          <label>Toggle Reveal Mode</label>
+          <p class="setting-desc">Show your real data in AI responses</p>
+        </div>
+        <code style="font-size:12px;background:#f3f4f6;padding:4px 8px;border-radius:4px">Alt+Shift+R</code>
+      </div>
+      <div class="setting-row">
+        <div>
+          <label>Toggle Silent Send on/off</label>
+          <p class="setting-desc">Quickly enable or disable all substitution</p>
+        </div>
+        <code style="font-size:12px;background:#f3f4f6;padding:4px 8px;border-radius:4px">Alt+Shift+S</code>
+      </div>
+      <p class="section-desc" style="margin-top:8px;margin-bottom:0">
+        To change these shortcuts:<br>
+        <strong>Chrome:</strong> <code>chrome://extensions/shortcuts</code><br>
+        <strong>Firefox:</strong> <code>about:addons</code> → gear icon → Manage Extension Shortcuts
+      </p>
+    </section>
+
     <section class="section">
       <h2>Settings</h2>
       <div class="setting-row">