feat(fana): C1 — núcleo del writer DAG editor (core + graph)

Primer paso de fana (prioridad alta entre las apps Fase C).

- fana-core — NarrativeAtom: id + content_hash SHA-256 + content
  Arc<String> (structural sharing: ramificar es O(1)) + semantic_vectors
  + dependencies + branch_id + CoherenceState (Valid/InConflict/
  PendingEvaluation). Invariante hash↔content verificable; set_content
  re-hashea y marca PendingEvaluation.
- fana-graph — NarrativeGraph: DAG de átomos + adjacency
  dependencia→dependientes. propagate_mutation: BFS que marca
  PendingEvaluation en cascada a todo descendiente (la "onda de choque
  lógica" de la spec), agnóstico de UI — devuelve los ids afectados.
  topological_order con detección de ciclo.

10 tests verdes. cargo check --workspace verde.
Pendiente fana: semantic (cliente verbo), store (sled), llm, render-plan,
editor-gpui.

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

Cargo.lock

@@ -3945,6 +3945,22 @@ version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7360491ce676a36bf9bb3c56c1aa791658183a54d2744120f27285738d90465a"
 
+[[package]]
+name = "fana-core"
+version = "0.1.0"
+dependencies = [
+ "sha2",
+ "uuid",
+]
+
+[[package]]
+name = "fana-graph"
+version = "0.1.0"
+dependencies = [
+ "fana-core",
+ "uuid",
+]
+
 [[package]]
 name = "fana-md"
 version = "0.1.0"