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>

tests/profiles/test_profile_integration.gd

@@ -0,0 +1,64 @@
+extends GutTest
+## Tests d'integration des autoloads ProfileManager / SaveManager /
+## ProgressManager : la "colle" fine entre la logique pure (deja testee
+## isolement) et la persistance reelle sur disque.
+
+var created_profile_ids: Array[String] = []
+
+
+func after_each() -> void:
+    for profile_id in created_profile_ids:
+        ProfileManager.delete_profile(profile_id)
+    created_profile_ids.clear()
+
+
+func test_create_and_select_profile_round_trips_through_disk() -> void:
+    var profile_id := ProfileManager.create_profile("Explorateur", "CE1")
+    created_profile_ids.append(profile_id)
+
+    assert_true(ProfileManager.select_profile(profile_id))
+    assert_eq(ProfileManager.current_profile_id, profile_id)
+
+    ProgressManager.record_attempt("accord_groupe_nominal", true, false, "multiple_choice")
+    assert_true(ProgressManager.save_now())
+
+    var reloaded: Variant = SaveManager.load(profile_id)
+    assert_not_null(reloaded)
+    assert_true(reloaded["skills"].has("accord_groupe_nominal"))
+
+
+func test_selecting_unknown_profile_fails_without_side_effects() -> void:
+    assert_false(ProfileManager.select_profile("profile_does_not_exist"))
+
+
+func test_two_profiles_are_isolated_through_the_autoload_layer() -> void:
+    var profile_a := ProfileManager.create_profile("Alice", "CE1")
+    var profile_b := ProfileManager.create_profile("Bob", "CE2")
+    created_profile_ids.append(profile_a)
+    created_profile_ids.append(profile_b)
+
+    ProfileManager.select_profile(profile_a)
+    ProgressManager.record_attempt("accord_groupe_nominal", true, false, "multiple_choice")
+    ProgressManager.save_now()
+
+    ProfileManager.select_profile(profile_b)
+    ProgressManager.record_attempt("homophones", false, true, "sentence_correction")
+    ProgressManager.save_now()
+
+    var save_a: Variant = SaveManager.load(profile_a)
+    var save_b: Variant = SaveManager.load(profile_b)
+    assert_true(save_a["skills"].has("accord_groupe_nominal"))
+    assert_false(save_a["skills"].has("homophones"))
+    assert_true(save_b["skills"].has("homophones"))
+    assert_false(save_b["skills"].has("accord_groupe_nominal"))
+
+
+func test_delete_profile_removes_it_from_disk_and_listing() -> void:
+    var profile_id := ProfileManager.create_profile("Explorateur", "CE1")
+
+    assert_true(ProfileManager.list_profiles().has(profile_id))
+
+    ProfileManager.delete_profile(profile_id)
+
+    assert_false(ProfileManager.list_profiles().has(profile_id))
+    assert_null(SaveManager.load(profile_id))