fix(companion): pack and history files from the card checked, contact loops skip the reserved slots, small UI fixes

- L2 vector packs: a damaged count can't wrap the index size, and an
  entry pointing past the file is refused.
- L2 map share-target list: sized for 40 long channel names and 16
  favourites (it could overflow), off the stack.
- L2 SD history: a file with an unreadable header is set aside as .bad
  instead of written over; Delete message history takes those too.
- Contact lookups by key or hash start after the reserved anon slots (an
  empty one matched a 00 hop hash with a blank name); MessagesScreen uses
  contactctl::hopName().
- Nearby keeps its selection by public key: deleting a contact shifts
  the table.
- ui-new Live Share target cycle holds every channel and favourite.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/ui-new/HomeScreen.h

@@ -1491,7 +1491,7 @@ public:
             }
           }
         } else if (prefix) {
-          for (int idx = 0; ; idx++) {
+          for (int idx = MAX_ANON_CONTACTS; ; idx++) {
             ContactInfo c;
             if (!the_mesh.getContactByIdx(idx, c)) break;
             if (memcmp(c.id.pub_key, prefix, NodePrefs::FAVOURITE_PREFIX_LEN) == 0) {
@@ -1673,7 +1673,7 @@ public:
           _task->openChannelHistory(pfx[0]);
           return true;
         }
-        for (int idx = 0; ; idx++) {
+        for (int idx = MAX_ANON_CONTACTS; ; idx++) {
           ContactInfo c2;
           if (!the_mesh.getContactByIdx(idx, c2)) break;
           if (memcmp(c2.id.pub_key, pfx, NodePrefs::FAVOURITE_PREFIX_LEN) == 0) {