tray: Tray.placeSig analogue of placeCard for SIG SELECT exit; rename arc-in → fade-in — TDD

After all 3 gamers in a polarity room confirm TAKE SIG and the 12s countdown
expires, sig-select.js's room:polarity_room_done handler now plays the same
tray-open / fade-in / tray-close sequence the role-select uses, then
dismisses the sig overlay & shows the waiting msg ("Gravity settling…" /
"Levity appraising…") on Tray.placeSig's completion callback. Visual order:
sig stage → tray slides in → sig fades into the second tray cell → tray
slides out → table hex w. waiting msg. Cross-polarity events (other room
finishing while we're still in our overlay) are no-op as before.

- tray.js: new Tray.placeSig(sourceEl, onComplete). Mutates the SECOND
  .tray-cell in place (sig slot), copies aria-label / data-energies /
  data-operations / corner-rank + suit-icon markup from the source
  .sig-stage-card, then runs the shared open → fade-in → close sequence.
  Extracted _runFadeInSequence helper so placeCard + placeSig share the
  same animation glue. reset() now also clears .tray-sig-card from cells.

- _tray.scss: .tray-sig-card.fade-in > .sig-stage-card animates via the
  existing tray-role-fade-in keyframes.

- sig-select.js polarity_room_done handler: Tray.placeSig(stageCard,
  _settle); _settle runs the existing _dismissSigOverlay + _showWaitingMsg.
  Falls back to immediate dismiss when Tray is undefined (test environments
  without the tray).

- arc-in → fade-in rename across tray.js, role-select.js, _tray.scss
  (incl. @keyframes tray-role-arc-in → tray-role-fade-in), TraySpec.js
  spec descriptions + assertions, & test_room_role_select.py docstrings.
  The original "arc-in" name suggested a curved-path animation; the actual
  behaviour is a 1s opacity fade, so fade-in is the accurate label.

- TraySpec: 10 new placeSig specs mirroring placeCard (second-cell mutation,
  data + markup copy, tabIndex, fade-in class, animationend-triggered close,
  onComplete callback, landscape parity, reset cleanup).

- SigSelectSpec: 3 new specs (Tray.placeSig called w. stageCard on own
  polarity; not called on other polarity; overlay dismiss deferred to the
  Tray.placeSig completion callback).

344 specs / 4 pending green; RoleSelectTrayTest FT still green.

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/functional_tests/test_room_role_select.py

@@ -564,7 +564,7 @@ class RoleSelectTest(FunctionalTest):
         self.wait_for(
             lambda: self.assertFalse(
                 self.browser.execute_script("return Tray.isOpen()"),
-                "Tray should close after arc-in sequence",
+                "Tray should close after fade-in sequence",
             )
         )
 
@@ -636,7 +636,7 @@ class RoleSelectTrayTest(FunctionalTest):
     def test_portrait_role_card_enters_topmost_grid_square(self):
         """Portrait: after confirming a role the first .tray-cell gets
         .tray-role-card; the grid still has exactly 8 cells; and the tray
-        opens briefly then closes once the arc-in animation completes."""
+        opens briefly then closes once the fade-in animation completes."""
         self.browser.set_window_size(390, 844)
         room = self._make_room()
         self.create_pre_authenticated_session("slot1@test.io")
@@ -669,7 +669,7 @@ class RoleSelectTrayTest(FunctionalTest):
         self.wait_for(
             lambda: self.assertFalse(
                 self.browser.execute_script("return Tray.isOpen()"),
-                "Tray should close after the arc-in sequence"
+                "Tray should close after the fade-in sequence"
             )
         )
 
@@ -709,7 +709,7 @@ class RoleSelectTrayTest(FunctionalTest):
         self.wait_for(
             lambda: self.assertFalse(
                 self.browser.execute_script("return Tray.isOpen()"),
-                "Tray should close after the arc-in sequence"
+                "Tray should close after the fade-in sequence"
             )
         )