Add the playable scene loop: boot through mission to reward

Wires every autoload up to a real UI: boot -> profile select/create
-> world map (three mission markers, positioned from data, not
hardcoded pixels) -> mission intro (narrative from data/missions/,
a new data type with its own schema) -> rule panel -> exercise host
-> one of the three exercise type scenes -> feedback panel -> reward
screen -> back to the map.

exercise_host is the only piece with real orchestration logic: picks
exercises via ExerciseEngine (now fully implemented, validating at
load like make validate-data does), validates answers through the
pure AnswerValidator/DictationAnalyzer, escalates aid over 3 attempts
via AttemptFlow, feeds DifficultyManager so adaptive difficulty is
actually wired in rather than dead code, and records every attempt
through ProgressManager. Every exercise-type scene (multiple_choice,
sentence_correction, dictation) only emits its answer by signal, per
the architecture invariant.

All child-facing text now comes from data/localization/fr.json via
UIText, not hardcoded in scripts or scenes. Getting that right
required extending SchemaValidator to support "additionalProperties"
as a schema (dynamic keys), which also closed a real gap: save.skills
was previously unvalidated against SkillState's actual shape.

16 new headless tests, including two integration tests that instance
exercise_host.tscn directly and drive it by emitting child-scene
signals, stopping short of the final scene transition (which would
tear down the test runner's own tree). Everything that needs a
screen -- layout at different sizes, touch, virtual keyboard, actual
audio playback (no .ogg files exist yet) -- is listed in the new
docs/testing/manual-checklist.md instead of claimed as verified.

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

scenes/profiles/profile_select.gd

@@ -0,0 +1,78 @@
+extends Control
+## Ecran de selection de profil : un profil par enfant, suppression avec
+## confirmation explicite (cahier des charges §9).
+
+var _pending_delete_profile_id: String = ""
+
+@onready var _title_label: Label = %TitleLabel
+@onready var _profile_list: VBoxContainer = %ProfileList
+@onready var _empty_state_label: Label = %EmptyStateLabel
+@onready var _new_profile_button: Button = %NewProfileButton
+@onready var _delete_confirm_dialog: ConfirmationDialog = %DeleteConfirmDialog
+
+
+func _ready() -> void:
+    _title_label.text = UIText.get_text("profile_select.title")
+    _new_profile_button.text = UIText.get_text("profile_select.new_profile_button")
+    _empty_state_label.text = UIText.get_text("profile_select.empty_state")
+    _delete_confirm_dialog.title = UIText.get_text("profile_select.delete_confirm_title")
+    _delete_confirm_dialog.dialog_text = UIText.get_text("profile_select.delete_confirm_message")
+    _delete_confirm_dialog.ok_button_text = UIText.get_text("profile_select.delete_confirm_yes")
+    _delete_confirm_dialog.cancel_button_text = UIText.get_text(
+        "profile_select.delete_confirm_no"
+    )
+
+    _new_profile_button.pressed.connect(_on_new_profile_pressed)
+    _delete_confirm_dialog.confirmed.connect(_on_delete_confirmed)
+
+    _refresh_profile_list()
+
+
+func _refresh_profile_list() -> void:
+    for child in _profile_list.get_children():
+        child.queue_free()
+
+    var summaries := ProfileManager.list_profile_summaries()
+    _empty_state_label.visible = summaries.is_empty()
+
+    for summary: Dictionary in summaries:
+        _profile_list.add_child(_build_profile_row(summary))
+
+
+func _build_profile_row(summary: Dictionary) -> Control:
+    var row := HBoxContainer.new()
+
+    var select_button := Button.new()
+    select_button.text = "%s (%s)" % [summary["display_name"], summary["school_level"]]
+    select_button.size_flags_horizontal = Control.SIZE_EXPAND_FILL
+    select_button.pressed.connect(_on_profile_selected.bind(summary["profile_id"]))
+    row.add_child(select_button)
+
+    var delete_button := Button.new()
+    delete_button.text = UIText.get_text("profile_select.delete_button")
+    delete_button.pressed.connect(_on_delete_requested.bind(summary["profile_id"]))
+    row.add_child(delete_button)
+
+    return row
+
+
+func _on_profile_selected(profile_id: String) -> void:
+    if ProfileManager.select_profile(profile_id):
+        GameManager.goto(GameManager.SCENE_WORLD_MAP)
+
+
+func _on_delete_requested(profile_id: String) -> void:
+    _pending_delete_profile_id = profile_id
+    _delete_confirm_dialog.popup_centered()
+
+
+func _on_delete_confirmed() -> void:
+    if _pending_delete_profile_id.is_empty():
+        return
+    ProfileManager.delete_profile(_pending_delete_profile_id)
+    _pending_delete_profile_id = ""
+    _refresh_profile_list()
+
+
+func _on_new_profile_pressed() -> void:
+    GameManager.goto(GameManager.SCENE_PROFILE_CREATE)