Redesign flag/report icons as vector assets and dock review panels inside their choice card

Flag question now uses a clean vector flag (dark/light SVG variants,
replacing a hand-drawn pixel-art icon that got muddied by the shared
toolbar icon-tint override). Report question is now a megaphone
instead of a second flag glyph, since both toolbar buttons looked
identical before.

The correct-answer explanation and the wrong-answer follow-up quiz
previously rendered as separate bordered boxes sitting below the
entire choice list. Both now dock inside their own choice's card:
the explanation panel reparents onto the correct choice's row, the
follow-up panel was already there but visually detached. A shared
_attached_panel_box style drops the shared border/corner between the
choice button and its panel so they read as one continuous card.

assets/icons/medmind/report-question-light.svg.import

@@ -2,7 +2,7 @@
 
 importer="texture"
 type="CompressedTexture2D"
-uid="uid://btqfcwm8c1ymy"
+uid="uid://gljo3k630b6f"
 path="res://.godot/imported/report-question-light.svg-d6a637ee28802ff5e54da98728d1db20.ctex"
 metadata={
 "vram_texture": false