Add merit node type (Scene 8 ceremony + achievement award)

A merit node awards a configured achievement (awards_flag) to the player
the moment the playthrough arrives on it, with node provenance, then
presents a ceremony. Migration 028 extends node_type + the component_key
CHECK and adds awards_flag; the runtime grants the flag in advance/goto/
new-game write paths; MeritHost renders the ceremony (a component_key can
supply a bespoke one, e.g. a 3D model). Verified: teleport to a merit node
auto-grants its achievement.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

migrations/028_merit_nodes.sql

@@ -0,0 +1,18 @@
+-- Merit nodes: a ceremony node that awards an achievement when the playthrough
+-- reaches it (Scene 8 — "The Barricelli Luggage"). The awarded flag is authored on
+-- the node; the runtime grants it on arrival with node provenance. Merit nodes may
+-- also carry a component_key for their ceremony presentation (e.g. a 3D model).
+
+ALTER TABLE osint.story_nodes DROP CONSTRAINT story_nodes_node_type_check;
+ALTER TABLE osint.story_nodes ADD CONSTRAINT story_nodes_node_type_check
+  CHECK (node_type IN ('cutscene','dialogue','level','det_gate','llm_gate','merit'));
+
+-- Let a merit node carry a ceremony component_key (was cutscene/gate only).
+ALTER TABLE osint.story_nodes DROP CONSTRAINT story_nodes_check1;
+ALTER TABLE osint.story_nodes ADD CONSTRAINT story_nodes_check1
+  CHECK (component_key IS NULL OR node_type IN ('cutscene','det_gate','llm_gate','merit'));
+
+ALTER TABLE osint.story_nodes ADD COLUMN awards_flag TEXT
+  CHECK (awards_flag IS NULL OR awards_flag ~ '^[a-z][a-z0-9_.-]{0,63}$');
+ALTER TABLE osint.story_nodes ADD CONSTRAINT story_nodes_awards_flag_type
+  CHECK (awards_flag IS NULL OR node_type = 'merit');