migrate: remove patch system, adopt direct source ownership

BREAKING CHANGE: The patch-based build system is removed.
All Red Bear source now lives in local/sources/<component>/ as git repos.

Changes:
- src/recipe.rs: remove patches field from SourceRecipe::Git/Tar, add Local variant
- src/cook/fetch.rs: delete fetch_apply_patches, validate_patches, normalize_patch,
  fetch_compute_patches_hash, fetch_write_patches_state, fetch_patches_state_stale,
  fetch_validate_patch_symlinks, fetch_is_patches_newer. Simplify fetch and
  fetch_offline. Remove recipe_has_patches. Add Local source handler.
- src/bin/repo.rs: remove validate-patches command and handle_validate_patches
- 70 recipe.toml files: remove patches arrays, convert core recipes to Local source
- 272 .patch symlinks deleted from recipe directories
- integrate-redbear.sh: replace patch symlink logic with source fork validation
- Makefile: replace validate-patches with validate-sources target
- AGENTS.md: remove 369 lines of patch documentation, add source ownership model
- local/docs/PATCH-GOVERNANCE.md: deleted (replaced by SOURCE-OWNERSHIP-MODEL.md)
- local/docs/SOURCE-OWNERSHIP-MODEL.md: new canonical reference
- local/sources/: Red Bear fork repos created (kernel, relibc, base, bootloader,
  installer) from frozen 0.1.0 pre-patched archives
- .gitignore: exclude local/sources/ (separate git repos)
- create-forks.sh: new script for initializing fork repos

Build: cargo check passes (5 warnings, 0 errors).
Developer workflow is now: edit local/sources/ → repo cook → test. No patches.

recipes/dev/patch/recipe.toml

@@ -1,11 +1,6 @@
 [source]
 tar = "https://ftp.gnu.org/gnu/patch/patch-2.7.6.tar.xz"
 blake3 = "d46d14c12aa4ea51e356bf92091c368fd871e1d770b94bc29027886737aecd5f"
-patches = [
-    "01_no_rlimit.patch",
-    "02_no_chown.patch",
-    "03_renameat2.patch",
-]
 script = """
 wget -O build-aux/config.sub "https://gitlab.redox-os.org/redox-os/gnu-config/-/raw/master/config.sub?inline=false"
 autoreconf