Fase 0+1 cerradas: GNU grep 3.12 real construido e hidratado

Cierra el primer entregable del roadmap. Cambios:

- `Source`: ahora admite dos modos mutuamente excluyentes — `git` (repo+commit) o
  `tarball` (url+sha256). El hash de entrada del artefacto usa el commit en modo
  git y el sha256 en modo tarball; ambos son identificadores inmutables del
  contenido fuente. Validación en `Source::kind()` con error claro.
- `fetch`: dispatch por modo. Tarball cacheado en `work/tarballs/<sha>.tar`,
  descarga vía `curl -fL`, verificación sha256 con `sha2`, extracción con
  `--strip-components` (default 1, GNU-style).
- `recipes/grep.toml`: GNU grep 3.12 desde el tarball release de gnu.org
  (sha256 fijado, sin patches, `--disable-perl-regexp --disable-nls`).
- Bootstrap: añade `binutils` al rootfs Alpine — configure de autotools mira
  ld/ar/ranlib incluso cuando el compilador real es zig cc.
- `.gitignore`: `/work/` (artefactos transitorios del build).
- `docs/10-roadmap.md`: Fase 0 y Fase 1 marcadas ✅; entregable cerrado.

Nota sobre v3.11 vs v3.12: probé primero v3.11 y el binario producido daba
"memory exhausted" en cualquier regex (bug conocido de grep+musl static al
inicializar DFA). v3.12 corrige y funciona limpio dentro del rootfs Alpine.

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

Cargo.lock

@@ -96,7 +96,16 @@ dependencies = [
  "cc",
  "cfg-if",
  "constant_time_eq",
- "cpufeatures",
+ "cpufeatures 0.3.0",
+]
+
+[[package]]
+name = "block-buffer"
+version = "0.10.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3078c7629b62d3f0439517fa394996acacc5cbc91c5a20d8c658e77abd503a71"
+dependencies = [
+ "generic-array",
 ]
 
 [[package]]
@@ -167,6 +176,15 @@ version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3d52eff69cd5e647efe296129160853a42795992097e8af39800e1060caeea9b"
 
+[[package]]
+name = "cpufeatures"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "59ed5838eebb26a2bb2e58f6d5b5316989ae9d08bab10e0e6d103e656d1b0280"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "cpufeatures"
 version = "0.3.0"
@@ -176,6 +194,26 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "crypto-common"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78c8292055d1c1df0cce5d180393dc8cce0abec0a7102adb6c7b1eef6016d60a"
+dependencies = [
+ "generic-array",
+ "typenum",
+]
+
+[[package]]
+name = "digest"
+version = "0.10.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ed9a281f7bc9b7576e61468ba615a66a5c8cfdff42420a70aa82701a3b1e292"
+dependencies = [
+ "block-buffer",
+ "crypto-common",
+]
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -210,6 +248,16 @@ version = "0.1.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
 
+[[package]]
+name = "generic-array"
+version = "0.14.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85649ca51fd72272d7821adaf274ad91c288277713d9c18820d8499a7ff69e9a"
+dependencies = [
+ "typenum",
+ "version_check",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.4.2"
@@ -229,6 +277,8 @@ version = "0.0.1"
 dependencies = [
  "anyhow",
  "hammer-core",
+ "hex",
+ "sha2",
  "tempfile",
  "thiserror",
  "tracing",
@@ -293,6 +343,12 @@ version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
 
+[[package]]
+name = "hex"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
+
 [[package]]
 name = "id-arena"
 version = "2.3.0"
@@ -536,6 +592,17 @@ dependencies = [
  "unsafe-libyaml",
 ]
 
+[[package]]
+name = "sha2"
+version = "0.10.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a7507d819769d01a365ab707794a4084392c824f54a7a6a7862f8c3d0892b283"
+dependencies = [
+ "cfg-if",
+ "cpufeatures 0.2.17",
+ "digest",
+]
+
 [[package]]
 name = "sharded-slab"
 version = "0.1.7"
@@ -718,6 +785,12 @@ dependencies = [
  "tracing-log",
 ]
 
+[[package]]
+name = "typenum"
+version = "1.20.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6f5e870be6c3b371b77fe0ee0bafb859fa4964b4404c27de1d380043c4dda20"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.24"
@@ -748,6 +821,12 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
 
+[[package]]
+name = "version_check"
+version = "0.9.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
+
 [[package]]
 name = "wasip2"
 version = "1.0.3+wasi-0.2.9"