feat: R-minor-sensitive binary builds (full + iterative) (#84)

## Summary

Builds R-minor-sensitive CRAN packages once per installed R minor version (into per-minor S3 slots `…/contrib/<x.y>/`) and everything else once into the generic slot, driven by bincraft 4.2.0's ABI classifier. Both the full and iterative pipelines are covered.

## What's in here

**Detection / precompute**

- `local/r-minor-helpers.R` — pure `classify_from_metadata()` (NeedsCompilation / risky `LinkingTo`) + `parse_build_args()`, with unit tests.
- `local/packages-to-build.R` — adds a per-package `r_minor_sensitive` flag: cheap CRAN-metadata rules first, source download + `bincraft::needs_per_minor_recompile()` only for the ambiguous compiled subset (fail-safe to sensitive). Classified once per package, applied to all versions.

**Full build**

- `local/build-all.R` — passes the per-row `is_r_minor_sensitive` flag; new `--sensitive-only` mode builds just the risky subset.
- `.crow/build-all-versions-{amd64,arm64}.yaml` — install-deps persists the sensitive subset; build step runs a sensitive-only pass under each non-primary `/opt/R/*` minor; new step uploads the generic index plus a per-minor index for each minor.

**Iterative build**

- All 14 `.crow/process-updates-*.yaml` — primary pass uses `r_minor_detection = 'classifier'`; a sensitive-only multi-R pass builds risky updates under each other minor; per-minor index upload added.

**Tooling / housekeeping**

- Pins bincraft `v4.1.1` → `v4.2.0` across all workflows; removes the superseded standalone `build-r-minor-sensitive-packages.yaml`.
- Adds prek/pre-commit hooks (prettier, markdownlint, editorconfig-checker, yamllint, air) and applies them repo-wide; excludes the verbatim GPL `LICENSE.md` and auxiliary shell scripts.
- Design + implementation docs under `docs/superpowers/`.

## Requires before merge

- A `v4.2.0` git tag must be pushed on the bincraft repo (codefloe.com/rpkgs/bincraft) — the workflow install steps pin `@v4.2.0`. The full-build install-deps clones `main`, so it is unaffected.

Reviewed-on: #84

.pre-commit-config.yaml

@@ -0,0 +1,45 @@
+# cSpell:ignore autofix autoupdate
+# Excluded: verbatim GPL license and auxiliary shell scripts with intentional
+# in-string formatting (reformatting would corrupt their output).
+exclude: |
+  (?x)^(
+    LICENSE\.md|
+    benchmark/|
+    docker/reprex/
+  )
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v6.0.0
+    hooks:
+      - id: end-of-file-fixer
+      - id: trailing-whitespace
+        args:
+          - --markdown-linebreak-ext=md
+  - repo: https://github.com/DavidAnson/markdownlint-cli2
+    rev: v0.22.1
+    hooks:
+      - id: markdownlint-cli2
+  - repo: https://github.com/rbubley/mirrors-prettier
+    rev: v3.8.4
+    hooks:
+      - id: prettier
+  - repo: https://github.com/posit-dev/air-pre-commit
+    rev: 0.8.2
+    hooks:
+      - id: air-format
+  - repo: https://github.com/editorconfig-checker/editorconfig-checker
+    rev: v3.7.0
+    hooks:
+      - id: editorconfig-checker
+  - repo: https://github.com/adrienverge/yamllint.git
+    rev: v1.38.0
+    hooks:
+      - id: yamllint
+        args: [--strict, -c=.yamllint.yaml]
+  - repo: local
+    hooks:
+      - id: yaml-file-extension
+        name: Check if YAML files has *.yaml extension.
+        entry: YAML filenames must have .yaml extension.
+        language: fail
+        files: .yml$