Fase 3 — diario de mutaciones (hammer-journal + fanotify + hammer journal)

Nuevo crate hammer-journal y watcher fanotify en hammerd. Cierra el contrato
del SDD 05 §3 ("toda mutación trazable/opaca registrada y consultable") y
liquida la deuda Fase 2 sobre el hook al diario en commit.

hammer-journal:
- MutationEvent (op, path, by, content_hash?, note?), MutationOp
  Create/Replace/Edit/Delete, Source enum tagged HammerHydrate /
  HammerCommit / External (distingue trazable de opaco para `export`).
- Journal: record append-only + sync_data, read_all/tail/follow (offset),
  resilencia a líneas malformadas (kernel-panic mid-write se ignora).
- RFC 3339 UTC sin chrono (Hinnant civil_from_days, válido para todo i64).
- 7 unit tests cubren append/read/tail/follow/malformed/serde/timestamp.

Watcher (hammerd):
- nix::sys::fanotify con FAN_CLASS_NOTIF + FAN_CLOSE_WRITE +
  FAN_EVENT_ON_CHILD sobre /bin /sbin /usr/bin /usr/sbin /lib /usr/lib /etc.
- Resuelve path por readlink(/proc/self/fd/<n>) — sin FAN_REPORT_DFID_NAME
  para Fase 3 v1; el refinamiento Create/Edit con metadata viene después.
- Filtro: hammer_overlay::status(state_root) → ignora paths bajo un overlay
  activo (el ruido del experimento no entra hasta el commit).
- Sin CAP_SYS_ADMIN, fanotify_init falla; hammerd lo reporta y sigue
  durmiendo (preparado para que Fase 5 monte el bus encima).
- 3 unit tests sobre defaults/filtros/uid lookup.

CLI:
- hammer journal [--dir] [--tail N] [--follow] [--format pretty|json].
- hammer commit registra cada archivo promocionado/removido vía
  commit_with_journal; --no-journal opt-out.

Hook overlay::commit:
- commit_with_journal(id, root, journal): para cada copied/removed emite un
  MutationEvent con Source::HammerCommit { overlay }. Test directo del hook
  sin overlayfs (lógica pura) más el e2e existente que ya cubre los mounts.

57 tests workspace, 0 fallos.

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

Cargo.lock

@@ -124,6 +124,12 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
 
+[[package]]
+name = "cfg_aliases"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
+
 [[package]]
 name = "clap"
 version = "4.6.1"
@@ -293,7 +299,9 @@ dependencies = [
  "clap",
  "hammer-build",
  "hammer-core",
+ "hammer-journal",
  "hammer-overlay",
+ "serde_json",
  "tracing",
  "tracing-subscriber",
 ]
@@ -312,12 +320,27 @@ dependencies = [
  "toml",
 ]
 
+[[package]]
+name = "hammer-journal"
+version = "0.0.1"
+dependencies = [
+ "anyhow",
+ "hammer-core",
+ "serde",
+ "serde_json",
+ "tempfile",
+ "thiserror",
+ "tracing",
+]
+
 [[package]]
 name = "hammer-overlay"
 version = "0.0.1"
 dependencies = [
  "anyhow",
  "hammer-core",
+ "hammer-journal",
+ "libc",
  "serde",
  "serde_json",
  "tempfile",
@@ -333,6 +356,12 @@ dependencies = [
  "anyhow",
  "clap",
  "hammer-core",
+ "hammer-journal",
+ "hammer-overlay",
+ "libc",
+ "nix",
+ "tempfile",
+ "thiserror",
  "tracing",
  "tracing-subscriber",
 ]
@@ -439,6 +468,18 @@ version = "2.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6b947ae49db0d222b1dbc6b113ce7248a3fc3a6ca21b696717bfc000ba4484d8"
 
+[[package]]
+name = "nix"
+version = "0.30.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "74523f3a35e05aba87a1d978330aef40f67b0304ac79c1c00b294c9830543db6"
+dependencies = [
+ "bitflags",
+ "cfg-if",
+ "cfg_aliases",
+ "libc",
+]
+
 [[package]]
 name = "nu-ansi-term"
 version = "0.50.3"