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/SKILL.md

@@ -51,7 +51,7 @@ So:
 ## Where the pin is looked for
 
 One search order, written once in `scripts/pin.py` and imported by both the
-`tea-guard` hook and the sync/wiki transport — they cannot disagree about a
+`tea-guard` hook and the sync transport — they cannot disagree about a
 directory, and a test asserts neither keeps a copy of the walk.
 
 `$CLAUDE_PROJECT_DIR`, then the caller's hint (the hook passes the Bash call's