Restructure tea skill into a plugin with a mandatory-login guard

Convert the standalone `tea` skill into a skills-dir plugin so commands are
namespaced and an enforcement hook can ship with it:

- /tea:login  — pin the project Gitea login into .claude/settings.local.json
- /tea:use    — tea CLI reference (was the old root SKILL.md), with the
                login rule slimmed since the hook now enforces it
- hooks/tea-guard.sh — PreToolUse(Bash) guard: blocks any `tea` command that
  touches Gitea unless it carries --login and $GITEA_LOGIN is set. Exempts
  `tea logins list` and `tea --version/--help` so /tea:login can bootstrap.

References moved under skills/use/references/. `claude plugin validate` passes;
guard unit-tested across allow/block cases.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skills/use/references/tea/misc.md

@@ -0,0 +1,17 @@
+# tea CLI — MISCELLANEOUS
+
+See [`./index.md`](./index.md) for global options and common flags shared by all commands.
+
+## `tea whoami`
+Show the currently logged in user.
+
+## `tea admin, a`
+Operations requiring admin access on the Gitea instance.
+
+### `tea admin users` (alias: `u`)
+Fields: `id,login,full_name,email,avatar_url,language,is_admin,restricted,prohibit_login,location,website,description,visibility,activated,lastlogin_at,created_at`.
+
+- `list, ls`
+- `create, add, new` — `--username/-u`, `--password/-p` / `--password-file` / `--password-stdin`, `--email/-e`, `--full-name`, `--admin`, `--restricted`, `--prohibit-login`, `--no-must-change-password`, `--visibility {public|limited|private}`.
+- `edit, update, e, u <username>` — paired flags: `--password` (or `--password-file`/`--password-stdin`), `--email/-e`, `--full-name`, `--description`, `--website`, `--location`, `--admin`/`--no-admin`, `--restricted`/`--no-restricted`, `--prohibit-login`/`--allow-login`, `--active`/`--inactive`, `--no-must-change-password`, `--visibility`, `--max-repo-creation` (-1 = unlimited), `--allow-git-hook`/`--no-allow-git-hook`, `--allow-import-local`/`--no-allow-import-local`, `--allow-create-organization`/`--no-allow-create-organization`.
+- `delete, rm, remove <username>` — `--confirm/-y`.