Flip Elsewhen between Fahrenheit and Celsius with Alt+T (#13450)

* Flip Elsewhen between Fahrenheit and Celsius with Shift+T

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

* Flip Elsewhen's temperature units with Alt+T instead of Shift+T

PanelKeyCatcher's textKey now carries the held modifiers, which is how the
panel tells Alt+T from T. Existing handlers take only the text and are
unaffected.

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

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/shell.d/panel-key-catcher-test.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
+
+# /usr/bin/qmltestrunner is the Qt 5 binary, which exits 0 having run nothing.
+qml_test_runner=""
+for candidate in /usr/lib/qt6/bin/qmltestrunner /usr/lib/qt6/qmltestrunner; do
+  if [[ -x $candidate ]]; then
+    qml_test_runner=$candidate
+    break
+  fi
+done
+
+if [[ -z $qml_test_runner ]]; then
+  skip "qt6 qmltestrunner not found; skipping panel key catcher tests"
+  exit 0
+fi
+
+output=$(QT_QPA_PLATFORM=offscreen QT_QUICK_BACKEND=software "$qml_test_runner" -input "$SHELL_TEST_DIR/panel-key-catcher/qml" -o -,txt 2>&1) ||
+  fail "panel key catcher passes modifiers with text keys" "$output"
+pass "panel key catcher passes modifiers with text keys"