feat(edit): add guests from the contact picker

Close the name-on-manual-add gap. The add-guest row gains a "from
contacts" button that launches the system contact picker (ACTION_PICK on
ContactsContract Email URI); the picked email row is queried for
Email.ADDRESS + DISPLAY_NAME, so a chosen guest gets both email and name
in one tap. No READ_CONTACTS — the result Intent grants temporary read
access to just that row, so Calendula stays no-permission/no-network. The
inline email field remains the quick email-only path. Mark the roadmap
item shipped.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/res/values/strings.xml

@@ -81,6 +81,7 @@
     <string name="event_edit_attendees">Guests</string>
     <string name="event_edit_add_guest">Add guest</string>
     <string name="event_edit_add_guest_hint">Add a guest by email…</string>
+    <string name="event_edit_add_guest_from_contacts">Add from contacts</string>
     <string name="event_edit_remove_guest">Remove guest</string>
     <string name="event_edit_attendee_required">Required</string>
     <string name="event_edit_attendee_optional">Optional</string>