Add profile and save persistence, wired into the three autoloads

scripts/profiles/: SaveIO handles real file I/O in user://saves (one
file per profile_id, atomic write via temp-file-then-rename, backup
copy before each overwrite, corrupted-main falls back to backup,
schema-invalid content is rejected like corruption). SaveMigration
and SaveFactory are pure; SaveMigration refuses a schema_version it
doesn't recognize (older or newer) rather than guessing. ProgressUpdates
is pure and wires ReviewScheduler/DifficultyManager onto a save's
skills dict, including per-session overdue-review marking.

The three autoloads (SaveManager, ProfileManager, ProgressManager)
stay thin: in-memory current-profile state and orchestration only,
no logic of their own, so the actual behavior lives in the tested
pure/file-IO modules above rather than in untestable glue.

26 new headless tests, including the failure modes called out in the
launch prompt: a truncated .tmp file never corrupts the readable
save, a corrupted main file falls back to its backup, two profiles
never mix (down through the real autoload layer, not just SaveIO),
and an unknown future schema_version is rejected outright.

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

scripts/profiles/progress_updates.gd

@@ -0,0 +1,60 @@
+class_name ProgressUpdates
+extends RefCounted
+## Fonctions pures qui appliquent une tentative d'exercice ou un debut de
+## seance a une sauvegarde (dictionnaire conforme a save.schema.json), en
+## s'appuyant sur ReviewScheduler et DifficultyManager (scripts/pedagogy/).
+## ProgressManager (autoload) est seul responsable d'appeler ces fonctions et
+## de persister le resultat via SaveManager ; l'ecriture sur disque reste
+## groupee en fin de mission (docs/specs/decisions.md, point 7).
+
+
+## attempt : {"skill": String, "success": bool, "hint_used": bool,
+## "exercise_type": String}.
+static func record_attempt(save_data: Dictionary, attempt: Dictionary) -> Dictionary:
+    var updated: Dictionary = save_data.duplicate(true)
+    var skills: Dictionary = updated["skills"]
+    var skill_id: String = attempt["skill"]
+    var skill_state: Dictionary = (
+        skills[skill_id] if skills.has(skill_id) else ReviewScheduler.initial_state()
+    )
+    var current_session: int = updated["session_count"]
+    skills[skill_id] = ReviewScheduler.record_attempt(skill_state, attempt, current_session)
+    updated["skills"] = skills
+    return updated
+
+
+## A appeler une fois en debut de seance, avant toute tentative : incremente
+## session_count et bascule en "a_reviser" les competences "acquise" dont le
+## delai de revision est depasse sans nouvelle pratique.
+static func start_session(save_data: Dictionary) -> Dictionary:
+    var updated: Dictionary = save_data.duplicate(true)
+    updated["session_count"] = int(updated["session_count"]) + 1
+    var current_session: int = updated["session_count"]
+
+    var skills: Dictionary = updated["skills"]
+    var updated_skills: Dictionary = {}
+    for skill_id: String in skills:
+        updated_skills[skill_id] = ReviewScheduler.mark_overdue_as_review(
+            skills[skill_id], current_session
+        )
+    updated["skills"] = updated_skills
+    return updated
+
+
+static func next_difficulty_for_skill(
+    save_data: Dictionary, skill_id: String, current_difficulty: int
+) -> int:
+    var skills: Dictionary = save_data["skills"]
+    if not skills.has(skill_id):
+        return current_difficulty
+    var recent: Array[bool] = skills[skill_id]["recent_results"]
+    return DifficultyManager.next_difficulty(current_difficulty, recent)
+
+
+static func unlock_region(save_data: Dictionary, region_id: String) -> Dictionary:
+    var updated: Dictionary = save_data.duplicate(true)
+    var regions: Array = updated["unlocked_regions"]
+    if not regions.has(region_id):
+        regions.append(region_id)
+    updated["unlocked_regions"] = regions
+    return updated