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/labels.py

@@ -32,6 +32,11 @@ created by push as they come up, and deleting or renaming anything at all.
 Only repository labels are read; an organization's own labels sit behind a
 different endpoint and are neither read nor written.
 
+The issue store is out of scope too, and not incidentally. A label belongs to
+the repository, not to any issue, so this command neither reads tmp/issues/ nor
+creates it — the taxonomy it paints comes from the domain MODULE, and the
+request bodies it sends go to the transport's own tmp/payload/.
+
 Login: the operator's pin from .claude/settings.local.json (see /tea:auth).
 """
 import argparse
@@ -185,8 +190,7 @@ def main():
                 continue
             payload = dict(spec, name=name)
             new = _gitea.api(login, "%s/labels" % base, "POST", payload,
-                             payload_name="label-%s" % name.replace("/", "-"),
-                             out_root=issue.ISSUE_ROOT)
+                             payload_name="label-%s" % name.replace("/", "-"))
             if not new or "id" not in new:
                 _gitea.die("could not create label %r" % name)
             print("created  %-20s id %-5s %s%s" % (name, new["id"], spec["color"], mark))
@@ -211,8 +215,7 @@ def main():
         for field, _is, _want in drift:
             patch[field] = spec[field]
         _gitea.api(login, "%s/labels/%s" % (base, got.get("id")), "PATCH", patch,
-                   payload_name="label-%s" % name.replace("/", "-"),
-                   out_root=issue.ISSUE_ROOT)
+                   payload_name="label-%s" % name.replace("/", "-"))
         fixed += 1
         print("fixed    %-20s id %-5s %s" % (name, got.get("id"), shown))