feat: pre-send PPI detection — warns while typing, auto-add mappings

Like spellcheck for privacy. Scans text as you type and paste
into chat inputs (debounced 800ms). Shows a dark floating warning
panel listing detected PPI BEFORE you hit Enter.

Each detected item has a green [+] button that instantly:
1. Generates a plausible fake value (random IP, fake address, etc.)
2. Adds it as a mapping to storage
3. Shows a checkmark to confirm

The warning disappears when you clear the text or when all
detected items have been addressed.

Three new Options toggles:
- Auto-detect unconfigured PPI (on by default)
- Offer to auto-add detected PPI (on by default)

Also adds a storage bridge (postMessage) so the page-world
content script can read/write chrome.storage through the
injector.

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/content/content.css

@@ -136,6 +136,90 @@
   font-style: italic;
 }
 
+/* Pre-send PPI warning (spellcheck-style, appears while typing) */
+.ss-presend-warning {
+  position: fixed;
+  top: 16px;
+  right: 16px;
+  max-width: 420px;
+  background: #1a1a1a;
+  color: #e5e7eb;
+  border: 1px solid #f59e0b;
+  border-radius: 10px;
+  padding: 12px 16px;
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+  font-size: 12px;
+  z-index: 999999;
+  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
+  opacity: 0;
+  transform: translateY(-10px);
+  transition: opacity 0.2s, transform 0.2s;
+  pointer-events: none;
+}
+
+.ss-presend-warning.visible {
+  opacity: 1;
+  transform: translateY(0);
+  pointer-events: auto;
+}
+
+.ss-ps-item {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  padding: 4px 0;
+  border-bottom: 1px solid #333;
+}
+
+.ss-ps-item:last-of-type { border-bottom: none; }
+
+.ss-ps-type {
+  font-size: 9px;
+  font-weight: 600;
+  color: #f59e0b;
+  min-width: 65px;
+  text-transform: uppercase;
+}
+
+.ss-ps-value {
+  font-family: 'SF Mono', Monaco, monospace;
+  font-size: 11px;
+  color: #4ade80;
+  background: #0a0a0a;
+  padding: 2px 6px;
+  border-radius: 4px;
+  max-width: 140px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.ss-ps-hint {
+  font-size: 10px;
+  color: #9ca3af;
+  flex: 1;
+}
+
+.ss-ps-add {
+  background: none;
+  border: 1px solid #4ade80;
+  border-radius: 4px;
+  color: #4ade80;
+  font-size: 14px;
+  font-weight: bold;
+  width: 24px;
+  height: 24px;
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  flex-shrink: 0;
+  padding: 0;
+}
+
+.ss-ps-add:hover { background: rgba(74, 222, 128, 0.15); }
+.ss-ps-add:disabled { border-color: #333; cursor: default; }
+
 /* Floating reveal mode indicator */
 .ss-reveal-badge {
   position: fixed;