feat(progression): composition root and event republisher (slice 9)

ProgressionRoot autoload builds the JSON stores from
GlobalizePath("user://"), loads the Profile, reads the authored upgrade
tables into a SkillCatalogue, and owns the ProgressionService. Every
mutating operation is wrapped so draining and republishing cannot be
forgotten - the one risk of the DrainEvents design, now confined to one
file.

ProgressionEventRepublisher turns domain records into EventBus signals
(ADR-0004), so existing subscribers and scene wiring keep working. New
RunEnded signal: GameOverScreen reads Lives directly today, which is the
last-life soft-lock.

Registered after SkillManager, since the skill catalogue is built from
AvailableSkills. GameStateStore stays until slice 10 moves the callers.

Transitional: LevelStarted is republished with a catalogue index because
GhostManager names files ghost_level_{index}.json.

objects/progression_root.tscn

@@ -0,0 +1,9 @@
+[gd_scene load_steps=3 format=3]
+
+[ext_resource type="Script" path="res://Autoloads/ProgressionRoot.cs" id="1_script"]
+[ext_resource type="Resource" path="res://resources/levels/level_catalogue.tres" id="2_catalogue"]
+
+[node name="ProgressionRoot" type="Node"]
+script = ExtResource("1_script")
+Catalogue = ExtResource("2_catalogue")
+StartingLives = 3