feat(local): auto-propose registry patches and track the feedback loop

Implement steps 3 + 4 of issue #115 on top of the failure classifier, now
that bincraft v4.4.3 applies registry patches/makevars/configure_args to the
target build (not just dependencies), so a trial patched build is meaningful.

- refactor the classify helpers to expose a pure build_triage_report() and a
  list-returning entry builder; failing-builds-report.R now renders from it
- add local/propose-patches.R (step 3, "propose, do not apply"): emit a
  pre-filled registry.json entry for each classified, safe, unregistered
  failure, validate the candidate set against a temporary merged registry,
  and (only on request) --write it plus a proposals ledger, or --open-issue a
  Forgejo tracking issue; the human gate and validator/trial-build acceptance
  stay, and novel source diffs / unknown signatures are never proposed
- add local/trial-build-patch.R: isolated bincraft build of one package with
  the registry applied (no upload/archive/metadata) as the pre-merge gate
- add local/proposal-tracking.R + local/proposal-tracking-lib.R (step 4):
  signature hit rate, proposed-vs-merged, and retirement candidates, with the
  pure helpers covered by tests
- teach validate-patches.R optional PATCH_DIR/REGISTRY_FILE overrides so a
  candidate registry can be validated without touching the real one
- document the propose/trial-build/tracking workflow in local/patches/README.md

local/validate-patches.R

@@ -1,9 +1,17 @@
 #!/usr/bin/env Rscript
 # Validate local/patches/registry.json: schema, referenced patch files, and
 # ambiguous overlaps. Exits 1 on any problem. Used by pre-commit and CI.
+#
+# Defaults to local/patches/registry.json. To validate a candidate registry
+# without touching the real one (e.g. from the patch proposer), set:
+#   PATCH_DIR      directory patch-file paths resolve against (default local/patches)
+#   REGISTRY_FILE  registry.json to validate       (default <PATCH_DIR>/registry.json)
 
-dir <- "local/patches"
-registry_file <- file.path(dir, "registry.json")
+dir <- Sys.getenv("PATCH_DIR", unset = "local/patches")
+registry_file <- Sys.getenv(
+  "REGISTRY_FILE",
+  unset = file.path(dir, "registry.json")
+)
 if (!file.exists(registry_file)) {
   cat("No registry.json found; nothing to validate.\n")
   quit(status = 0L)
@@ -19,33 +27,47 @@ for (i in seq_along(reg)) {
   e <- reg[[i]]
   missing <- setdiff(required, names(e))
   if (length(missing) > 0L) {
-    errs <- c(errs, sprintf(
-      "entry %d (%s): missing %s", i,
-      if (is.null(e$package)) "?" else e$package, toString(missing)
-    ))
+    errs <- c(
+      errs,
+      sprintf(
+        "entry %d (%s): missing %s",
+        i,
+        if (is.null(e$package)) "?" else e$package,
+        toString(missing)
+      )
+    )
   }
   if (!is.null(e$patch)) {
     p <- file.path(dir, e$patch)
     if (!file.exists(p)) {
-      errs <- c(errs, sprintf("entry %d (%s): patch file '%s' missing",
-                              i, e$package, p))
+      errs <- c(
+        errs,
+        sprintf("entry %d (%s): patch file '%s' missing", i, e$package, p)
+      )
     }
   }
 }
 
 # Ambiguous overlap: two entries for the same package with identical platforms
 # and versions.
-keys <- vapply(reg, function(e) {
-  sprintf(
-    "%s|%s|%s",
-    or_q(e$package),
-    paste(sort(as.character(unlist(e$platforms))), collapse = ","),
-    or_q(e$versions)
-  )
-}, character(1L))
+keys <- vapply(
+  reg,
+  function(e) {
+    sprintf(
+      "%s|%s|%s",
+      or_q(e$package),
+      paste(sort(as.character(unlist(e$platforms))), collapse = ","),
+      or_q(e$versions)
+    )
+  },
+  character(1L)
+)
 dups <- keys[duplicated(keys)]
 if (length(dups) > 0L) {
-  errs <- c(errs, sprintf("ambiguous duplicate entries: %s", toString(unique(dups))))
+  errs <- c(
+    errs,
+    sprintf("ambiguous duplicate entries: %s", toString(unique(dups)))
+  )
 }
 
 if (length(errs) > 0L) {
@@ -53,4 +75,8 @@ if (length(errs) > 0L) {
   cat(paste0("  - ", errs, "\n"))
   quit(status = 1L)
 }
-cat(sprintf("Patch registry OK (%d %s).\n", length(reg), if (length(reg) == 1L) "entry" else "entries"))
+cat(sprintf(
+  "Patch registry OK (%d %s).\n",
+  length(reg),
+  if (length(reg) == 1L) "entry" else "entries"
+))