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/auth/scripts/pin.py

@@ -3,7 +3,7 @@
 pin.py — where the operator's Gitea login pin is, and how it is found.
 
 **The search order lives here and nowhere else.** The `tea-guard` hook imports
-this module; so does the transport every sync and wiki script runs on. Two
+this module; so does the transport every sync script runs on. Two
 copies of the order is exactly how a git worktree came to have a working hook
 and a dead transport in the same directory: `tea` resolved the login, the
 scripts said "no login pinned", and the error told the operator to pin what was