refactor!: drop the wiki and page layers

The plugin is issues and nothing else now. `skills/page` (the page-tree
domain) and `skills/wiki` (its bridge to a Gitea wiki) are gone, and
with them the issue domain's `wiki:` field — page titles were the only
thing that tied the two domains together, and a field the tracker has
no column for never came back from a pull anyway.

What is left is the shape AGENTS.md already claimed for the rest of the
repo: one domain, one bridge, one transport. The docs, the plugin
manifest, and tea-runner's skill table now say so too, and
test_payload_root walks the one script directory that remains.

Also removes openspec/config.yaml; nothing in the repo referenced it.

378 tests pass.

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

skills/issue/references/format.md

@@ -3,8 +3,7 @@
 Canonical format for every issue in this project, whether it ever reaches a
 tracker or not. Designed to be unambiguous for both humans and LLMs: fixed
 English section headers in a fixed order, verifiable acceptance criteria, one
-issue = one deliverable. Source spec: the project wiki
-([Issues-Workflow](https://git.noodles.cam/claude-skills/tea/wiki/Issues-Workflow)).
+issue = one deliverable.
 
 Nothing here depends on Gitea. How these files are mapped onto a tracker is the
 sync layer's business — see `/tea:sync`.
@@ -42,7 +41,6 @@ labels: [type/task, tech/sql]
 assignees: [naudachu]
 milestone: v0.2
 depends: [migrate-schema]
-wiki: [Simple Chains/Ideas/Chain core]
 origin: gitea
 branch: feat/wire-sqlc
 gitea: claude-skills/tea#42
@@ -64,7 +62,6 @@ url: https://git.noodles.cam/claude-skills/tea/issues/42
 | `assignees` | domain | logins; may be empty |
 | `milestone` | domain | title, or `none` |
 | `depends` | domain | ids this issue depends on — **the authoritative graph** |
-| `wiki` | domain | page **titles** this issue is written up in; may be empty. Titles, not URLs — a title is a name for a document and stays in this layer, a URL is tracker bookkeeping. `/tea:page` owns what those titles mean; `page_ls.py --titles` prints them. Set it with `issue_new.py --wiki "<title>"` (repeatable) or by editing the line. The tracker has no field for it, so it is never sent — and a pull, which merges nothing but checkbox state, does not bring it back |
 | `origin` | domain | `local`, or the name of a tracker this also lives in |
 | `gitea` | sync | the handle in that tracker: `owner/repo#N` |
 | `branch` | sync | the tracker's branch link (Gitea `ref`); push fills an empty one with the current git branch, and never overwrites a filled one |