Accept a proposal using its detected marker id, not always a letter

detected_id (map_vision.read_marker_id) was wired into ground-truth
logging but never actually consumed when accepting a proposal --
every accepted target/ally silently got an auto-assigned A/B/C letter
regardless of what number the game itself shows for that unit.
_accept_proposal now prefers detected_id when present, falling back to
auto-assign on a collision (two markers misread to the same id, or a
real id that happens to match one already assigned) -- a duplicate id
is worse than losing traceability to the game's own number for that
one accept. Targets/allies keep their own separate id namespace, same
as auto-assignment already does elsewhere.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/fenigma/app.py

@@ -748,10 +748,25 @@ class MainWindow(Adw.ApplicationWindow):
             return
         if type_ is None:
             type_ = icons.target_type_from_icon(proposal.unit) or TargetType.UNKNOWN
-        if proposal.side == "friendly":
-            self.board.add_ally(type_, coord)
+        is_ally = proposal.side == "friendly"
+        # Prefer the marker's own detected "#<N>" id (map_vision.read_marker_id,
+        # already past its own confidence floor by the time it's non-None)
+        # over an auto-assigned letter -- lets an accepted unit's id match
+        # what's actually on screen, rather than every accept silently
+        # becoming A/B/C regardless of what the game itself calls it.
+        # Falls back to auto-assign (id_=None) on a collision: two markers
+        # misread to the same id, or a real id that just happens to match
+        # one already auto-assigned, either way a duplicate id is worse
+        # than losing this one accept's traceability to the game's own
+        # number.
+        id_ = proposal.detected_id
+        existing = {a.id for a in self.board.allies} if is_ally else {t.id for t in self.board.targets}
+        if id_ in existing:
+            id_ = None
+        if is_ally:
+            self.board.add_ally(type_, coord, id_=id_)
         else:
-            self.board.add_target(type_, coord)
+            self.board.add_target(type_, coord, id_=id_)
         proposal.accepted = True
         proposal.confirmed_type = type_.name