### Task B1: Create the patch registry with the RcppParallel entry

**Files:**
- Create: `local/patches/registry.json`
- Create: `local/patches/README.md`

**Interfaces:**
- Produces: the curated registry consumed by bincraft's `patches` argument.

- [ ] **Step 1: Write the registry**

```json
[
  {
    "package": "RcppParallel",
    "versions": "*",
    "platforms": ["alpine", "ubuntu-2604"],
    "env": { "RCPP_PARALLEL_USE_TBB": "0" },
    "configure_args": [],
    "makevars": {},
    "patch": null,
    "reason": "bundled Intel TBB fails to build on musl and on newer toolchains (e.g. g++ 15 on ubuntu-2604); disabling TBB falls back to TinyThread"
  }
]
```

- [ ] **Step 2: Write the README**

`local/patches/README.md` documents the schema (copy the field table from `specs/2026-06-30-package-patching-design.md`), how to add an entry, and that source diffs go in `local/patches/<pkg>/<file>.patch` referenced by the `patch` field.

- [ ] **Step 3: Verify it parses**

Run: `Rscript -e 'x <- jsonlite::fromJSON("local/patches/registry.json", simplifyVector = FALSE); stopifnot(length(x) == 1L, x[[1]]$package == "RcppParallel"); cat("ok\n")'`
Expected: `ok`.

- [ ] **Step 4: Commit**

```bash
git add local/patches/registry.json local/patches/README.md
git commit -m "feat(patches): add patch registry with RcppParallel TBB workaround"
```

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