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>

crates/modules/fana/fana-store/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "fana-store"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+publish.workspace = true
+description = "fana — persistencia del grafo narrativo en un store key-value embebido (sled), serializado con bincode."
+
+[dependencies]
+fana-core = { path = "../fana-core" }
+fana-graph = { path = "../fana-graph" }
+sled = { workspace = true }
+bincode = { workspace = true }
+uuid = { workspace = true }
+thiserror = { workspace = true }
+
+[dev-dependencies]
+tempfile = { workspace = true }