feat: v0.3.0 — multiple entries per field, README setup guide

Identity fields now support multiple entries per type:
- Add unlimited names (first, last, middle, nickname), emails,
  usernames, hostnames, and phone numbers per profile
- "+ Add" button on each section, "x" to remove rows
- Names have a type selector (1st/Last/Mid/Nick)

README now includes:
- First-time setup walkthrough (step by step)
- Icon color legend (gray/black/blue/red)
- Keyboard shortcuts table
- Note that extension does nothing until configured

Also bumps version to 0.3.0 for Firefox re-signing.

https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw

src/popup/popup.css

@@ -310,13 +310,61 @@ body {
   margin-bottom: 4px;
 }
 
+.id-label-row {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: 6px;
+}
+
 .id-label {
   font-size: 11px;
   font-weight: 600;
   color: #374151;
   text-transform: uppercase;
   letter-spacing: 0.5px;
-  margin-bottom: 6px;
+}
+
+.btn-add {
+  background: none;
+  border: 1px solid #d1d5db;
+  border-radius: 4px;
+  padding: 2px 8px;
+  font-size: 10px;
+  font-weight: 500;
+  color: #6b7280;
+  cursor: pointer;
+}
+
+.btn-add:hover { background: #f3f4f6; color: #111; }
+
+.id-entry-row {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  margin-bottom: 3px;
+}
+
+.id-entry-row .input-sm { flex: 1; }
+
+.id-entry-row .btn-remove {
+  background: none;
+  border: none;
+  color: #d1d5db;
+  cursor: pointer;
+  font-size: 16px;
+  padding: 0 2px;
+  line-height: 1;
+}
+
+.id-entry-row .btn-remove:hover { color: #dc2626; }
+
+.id-type-label {
+  font-size: 9px;
+  color: #9ca3af;
+  text-transform: uppercase;
+  min-width: 28px;
+  text-align: center;
 }
 
 .id-row {