fix: keep request payloads out of the issue store

`labels.py` handed `_gitea.api` the issue store as a place to put the
request file, and on a checkout without a store that quietly created
`tmp/issues/.payload/`. Bootstrapping a repository's labels touches no
issue at all, so the one rule the store has — nothing materializes it as
a side effect of a write — was broken by an operation that has no
business knowing the store exists.

Where a request body goes was never the caller's decision to make. It is
now the transport's: `tmp/payload/`, resolved from `_gitea.py`'s own
location the way both domains resolve theirs, so every caller — sync and
wiki alike — writes to one directory whatever it was invoked from, and
`out_root` is gone from `api`, `add_dependency` and all six call sites.
The directory is created by the first write of a run and not before: a
`--dry-run` leaves nothing behind. `tmp/` is already gitignored.

The name carries the distinction the old path lost. A store holds the
only copy of something; this holds debris kept for a retry or a
post-mortem, and deleting it costs nothing. A dotdir sitting among an
issue's files claimed otherwise, and `ls tmp/issues` started lying about
what existed.

tests/test_payload_root.py runs the real `labels.py` in a throwaway repo
against a fake `tea` on PATH: no store appears, the payloads land in
tmp/payload/, a dry run writes nothing, and a run from a subdirectory
still resolves to the repo root. Two source checks keep the callers from
drifting apart again.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

skills/sync/scripts/push.py

@@ -334,12 +334,12 @@ def main():
         if sent_number:
             payload = gmap.to_payload(iss, label_ids, ms_id, include_state=True)
             got = _gitea.api(login, "%s/issues/%d" % (base, sent_number), "PATCH",
-                             payload, payload_name="issue-%s" % id, out_root=root)
+                             payload, payload_name="issue-%s" % id)
             verb = "updated"
         else:
             payload = gmap.to_payload(iss, label_ids, ms_id)
             got = _gitea.api(login, "%s/issues" % base, "POST", payload,
-                             payload_name="issue-%s" % id, out_root=root)
+                             payload_name="issue-%s" % id)
             verb = "created"
         # The gate. Below this line the local file is going to be deleted, so
         # anything short of a confirmed write has to stop the run here.
@@ -364,7 +364,7 @@ def main():
         if missing:
             _gitea.api(login, "%s/issues/%d/labels" % (base, number), "PUT",
                        {"labels": [label_ids[l] for l in iss.labels if l in label_ids]},
-                       payload_name="labels-%s" % id, out_root=root)
+                       payload_name="labels-%s" % id)
             _gitea.warn("%s: labels re-applied via PUT (%s)" % (id, ", ".join(missing)))
 
         # The in-memory issue is stamped even though its file is going: the rest
@@ -392,7 +392,7 @@ def main():
             for slug, (drepo, dnum) in wanted_links:
                 if not dnum or (drepo, dnum) in have:
                     continue
-                if _gitea.add_dependency(login, base, number, drepo, dnum, root):
+                if _gitea.add_dependency(login, base, number, drepo, dnum):
                     print("    depends on  %s#%d  (%s)" % (drepo, dnum, slug))
                 else:
                     _gitea.warn("%s: could not link #%d -> %s#%d (%s) — link it by "