feat(fana): fana-store — persistencia del grafo narrativo (sled)

- fana-core: NarrativeAtom + CoherenceState ahora Serialize/Deserialize
  (serde con feature rc para el Arc<String>; uuid con feature serde).
- fana-graph: + atoms() iterator + from_atoms() constructor.
- fana-store: GraphStore sobre sled. put/get/remove_atom por Uuid,
  serialización bincode. save_graph persiste átomo por átomo;
  load_graph reconstruye el grafo (la adjacency se re-cablea desde las
  dependencies de cada átomo).

7 tests verdes (roundtrip put/get/remove + save/load_graph preserva
estructura). cargo check --workspace verde.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.lock

@@ -3949,6 +3949,7 @@ checksum = "7360491ce676a36bf9bb3c56c1aa791658183a54d2744120f27285738d90465a"
 name = "fana-core"
 version = "0.1.0"
 dependencies = [
+ "serde",
  "sha2",
  "uuid",
 ]
@@ -3979,6 +3980,19 @@ dependencies = [
  "web-sys",
 ]
 
+[[package]]
+name = "fana-store"
+version = "0.1.0"
+dependencies = [
+ "bincode",
+ "fana-core",
+ "fana-graph",
+ "sled",
+ "tempfile",
+ "thiserror 2.0.18",
+ "uuid",
+]
+
 [[package]]
 name = "fastembed"
 version = "4.9.1"