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>

.claude-plugin/plugin.json

@@ -1,10 +1,10 @@
 {
   "name": "tea",
-  "description": "Gitea issues and wiki pages as local markdown, cleanly layered: /tea:issue works on issues offline (format, validation, dependency graph) and /tea:page turns a discussion's artifacts into a titled, ordered page tree; /tea:sync and /tea:wiki move each to and from Gitea; /tea:use is the CLI reference, the tea-runner subagent executes the scripts on a cheap model, and a PreToolUse hook blocks any command that would touch Gitea without the operator-pinned 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, the tea-runner subagent executes the scripts on a cheap model, and a PreToolUse hook blocks any command that would touch Gitea without the operator-pinned login.",
   "version": "2.2.0",
   "author": {
     "name": "naudachu"
   },
   "license": "MIT",
-  "keywords": ["gitea", "cli", "git", "issues", "wiki", "login-guard"]
+  "keywords": ["gitea", "cli", "git", "issues", "login-guard"]
 }