Sync text zoom preference through the account instead of local settings

Local user://settings.cfg meant zoom level didn't follow a student
across devices/browsers. Question bank and CCS text scale now live on
the user's study profile in Mongo (QuestionTextScale/CcsTextScale),
synced through a new PUT /api/profile/me/text-scale endpoint and the
existing preferences GET/cache already used for study preferences.

Both question_player.gd and ccs_service.gd read the synced value at
startup and react to AccountProfileService.profile_changed so a value
pulled down after login (or changed from another session) applies
without a restart. Backend validates the 0.85-1.35 range and updates
only the field(s) provided via a targeted $set, so it can't clobber
the other scale or the unrelated study-profile preferences.

scripts/ui/ccs_player.gd

@@ -58,6 +58,8 @@ func _ready() -> void:
 	resized.connect(_update_responsive_layout)
 	if not theme_service.theme_changed.is_connected(_on_theme_changed):
 		theme_service.theme_changed.connect(_on_theme_changed)
+	if not CCSService.text_scale_changed.is_connected(_apply_text_scale):
+		CCSService.text_scale_changed.connect(_apply_text_scale)
 	_apply_theme()
 	call_deferred("_update_responsive_layout")