refactor: split issue domain from Gitea transport

An issue was a Gitea row that happened to be cached locally: its identity
was the tracker's number (42.md), its dependencies were tracker numbers
(depends: [#12]), and a local issue existed only as a draft that push
deleted on success. Nothing could be planned or tracked without a tracker.

Split into layers, with knowledge flowing one way:

  skills/issue  DOMAIN  what an issue is: format, validation, dep graph
        ^               offline; stdlib imports only, no subprocess
        | imports
  skills/sync   BRIDGE  map.py    md <-> Gitea JSON, pure, no I/O
                        _gitea.py login pin, api, pagination, filters
  skills/use    REFERENCE  tea CLI docs for non-issue entities

skills/issue never imports skills/sync. Delete the sync layer and the
domain keeps working.

Identity is now a slug derived from the title (wire-sqlc-appclick.md) and
is stable across retitles and pushes. Tracker numbers live in a `gitea:`
field, never in a file name and never in `depends:`; the pair is indexed
in .remote.json, which is a cache over the files, not a second source of
truth.

Behavior changes:

- Pushing is additive. The file is never deleted; it gains gitea:/url:/
  synced: and origin: flips from local to gitea. `origin: local` is a
  durable state, not a pending one.
- Pushes go in topological order so dependencies get numbers first.
- The dependency graph is computed offline from `depends:` metadata; body
  prose is passed through unchanged in both directions rather than being
  rewritten between slugs and #N.
- `origin` is domain-owned (whether work exists elsewhere is a fact about
  the work); the handle and how to reach it stay with sync.

Script moves:

  issue_get.py   -> sync/pull.py
  issue_push.py  -> sync/push.py
  issue_list.py  -> sync/remote.py
  issue_index.py -> issue/issue_index.py
  _tea.py        -> split into issue/issue.py, sync/map.py, sync/_gitea.py

New: issue/issue_new.py, issue/issue_check.py, issue/issue_tree.py, and
sync/comment.py — comment posting was the last issue operation still
hand-rolled through raw `tea api`.

references/issue-format.md moves to skills/issue/references/format.md;
label hex colors move out of it into map.py, since a color is how a
tracker paints a chip, not what an issue is.

Verified: offline path end to end (new, check, tree, index, push
--dry-run) and read-only against Gitea (remote listing, pull with
mapping, comment guard). Write paths of push.py and comment.py are not
exercised here.

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

.claude-plugin/marketplace.json

@@ -7,7 +7,7 @@
     {
       "name": "tea",
       "source": "./",
-      "description": "Gitea CLI (tea) reference plus a mandatory-login guard. Ships /tea:auth, /tea:use, /tea:issue, issue scripts with a local greppable cache, and a PreToolUse hook that blocks any tea command that would touch Gitea without --login."
+      "description": "Gitea issues as local markdown, cleanly layered: /tea:issue works on issues offline (format, validation, dependency graph), /tea:sync moves them to and from Gitea, /tea:use is the CLI reference, and a PreToolUse hook blocks any command that would touch Gitea without the operator-pinned login."
     }
   ]
 }