fix(voice): say the quadrant is missing instead of "could not be read"

"ترمیم برای دندون دو" set the treatment type but reported the tooth as
unreadable. Nothing was misheard: position 2 arrived intact, with no
quadrant, because none was spoken — four teeth carry position 2 and the
resolver correctly refused to pick one. Only the label was wrong, and it
sent the clinician looking for a transcription fault.

Adds a tooth_missing_quadrant reason that names what is missing and shows
how to say it ("دو بالا راست"), and tells the model explicitly to report a
quadrant-less number with arch and side null rather than guessing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/messages/en.json

@@ -914,6 +914,7 @@
     "voiceUnresolved": {
       "not_permanent_tooth": "not a permanent tooth",
       "position_out_of_range": "not a valid tooth position",
+      "tooth_missing_quadrant": "quadrant not said — e.g. “upper right two”",
       "malformed": "could not be read",
       "span_not_same_arch": "a bridge cannot span both jaws",
       "unknown_catalog_code": "not in this clinic’s list",