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- Pins bincraft `v4.1.1` → `v4.2.0` across all workflows; removes the superseded standalone `build-r-minor-sensitive-packages.yaml`.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

.crow/build-all-versions-install-deps-arm64.yaml

@@ -9,7 +9,7 @@ labels:
 
 steps:
   - name: 'Install deps and bincraft'
-    image: "reg.devxy.io/rpkgs/build-env-${OS}:${OS_VERSION}"
+    image: 'reg.devxy.io/rpkgs/build-env-${OS}:${OS_VERSION}'
     pull: true
     environment:
       REPO_RO_TOKEN:
@@ -34,7 +34,7 @@ steps:
       - git clone -q https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
       - git clone -q https://codefloe.com/rpkgs/bincraft.git /tmp/bincraft
       - /opt/R/$R_VERSION/bin/R -q -e 'pak::sysreqs_db_update(); pak::local_install("/tmp/bincraft"); pak::pak(c("RPostgres", "s3fs", "data.table", "future", "jsonlite")); packageVersion("bincraft")'
-      - /opt/R/$R_VERSION/bin/R -q -e "source('local/packages-to-build.R'); saveRDS(pkgs, '/mnt/cache/packages/pkgs_to_build.rds'); sprintf('Precomputed %s package versions to build', nrow(pkgs))"
+      - /opt/R/$R_VERSION/bin/R -q -e "source('local/packages-to-build.R'); saveRDS(pkgs, '/mnt/cache/packages/pkgs_to_build.rds'); saveRDS(pkgs[r_minor_sensitive == TRUE], '/mnt/cache/packages/r_minor_sensitive_pkgs.rds'); sprintf('Precomputed %s package versions (%s r-minor-sensitive)', nrow(pkgs), nrow(pkgs[r_minor_sensitive == TRUE]))"
     backend_options:
       docker:
         resources: