fix(local): shell-quote git args in the auto-patch push and trial-build gate (#126)

## Problem

The first real `auto-apply-patches` run classified, limited to the top-10, and validated the candidate registry cleanly, then died at the push step:

```
Validating candidate registry:
  Patch registry OK (13 entries).
sh: syntax error: unexpected "("
Error in git("commit", "-m", ...): git commit -m feat(patches): auto-propose 10 registry entries ... failed
```

Root cause: R's `system2()` with captured output (`stdout=TRUE`) runs the command through `/bin/sh`, and the arguments were passed **unquoted**. The commit message `feat(patches): ...` contains `()`, which the shell tried to interpret. The same class of bug affects the `^{commit}` and `ref:path` git refs in the trial-build gate.

## Fix

`shQuote()` every git argument:
- `propose-patches.R` -- the `git()` helper used by `--open-pr` (commit, push, checkout).
- `trial-build-registry.R` -- the base-ref reads (`rev-parse ... ^{commit}`, `ls-tree`, `show ref:path`).

## Verification

- Reproduced against a real git repo: the unquoted call fails with status 2 (the same `unexpected "("`); the `shQuote`d call commits successfully, and `rev-parse HEAD^{commit}` resolves.
- 105 tests pass; all pre-commit hooks pass.

Everything else in that run was correct: 842,659 failing builds classified, RcppParallel's 895 dependents correctly reported as blocked (not proposed), top-10 tbb-stddef candidates selected, 69 deferred, registry validated. Only the shell quoting was broken.

Reviewed-on: #126

local/propose-patches.R

@@ -435,7 +435,9 @@ if (do_write) {
   save_ledger(merge_ledger(load_ledger(), new_ledger_records))
 
   git <- function(...) {
-    st <- system2("git", c(...), stdout = TRUE, stderr = TRUE)
+    # system2() with captured output runs via /bin/sh, so shell-quote every arg
+    # (commit messages contain "()", refs contain "^{}", etc.).
+    st <- system2("git", shQuote(c(...)), stdout = TRUE, stderr = TRUE)
     if (!identical(attr(st, "status"), NULL)) {
       stop(sprintf(
         "git %s failed:\n%s",

local/trial-build-registry.R

@@ -52,9 +52,16 @@ current <- if (file.exists(registry_file)) {
 # silently treating the base as empty would trial-build the WHOLE registry
 # instead of just the entries the branch adds.
 registry_rel <- "local/patches/registry.json"
+# system2() with captured output runs via /bin/sh, so shell-quote the git args
+# (refs contain "^{}" and ":" that the shell would otherwise mangle).
 ref_ok <- suppressWarnings(system2(
   "git",
-  c("rev-parse", "--verify", "--quiet", sprintf("%s^{commit}", base_ref)),
+  shQuote(c(
+    "rev-parse",
+    "--verify",
+    "--quiet",
+    sprintf("%s^{commit}", base_ref)
+  )),
   stdout = TRUE,
   stderr = FALSE
 ))
@@ -63,14 +70,14 @@ if (!is.null(attr(ref_ok, "status"))) {
 }
 in_base <- suppressWarnings(system2(
   "git",
-  c("ls-tree", base_ref, "--", registry_rel),
+  shQuote(c("ls-tree", base_ref, "--", registry_rel)),
   stdout = TRUE,
   stderr = FALSE
 ))
 file_in_base <- length(in_base) > 0L && any(nzchar(in_base))
 base_json <- suppressWarnings(system2(
   "git",
-  c("show", sprintf("%s:%s", base_ref, registry_rel)),
+  shQuote(c("show", sprintf("%s:%s", base_ref, registry_rel))),
   stdout = TRUE,
   stderr = FALSE
 ))