feat: add the tea-runner execution agent

The skills carry meaning, the scripts carry work. Splitting the second
half onto a cheap model keeps the main session's context for the part
that needs judgement.

tea-runner is a Haiku subagent with Bash/Read/Grep/Glob/Skill and
nothing else. It loads /tea:sync or /tea:issue for the command table
rather than carrying its own copy, so the skills stay the single source
of truth for the script surface.

It executes and reports; it decides nothing. No Edit and no Write, so an
issue body is out of reach. No raw tea, no --force, no closing or
retitling, no pushing past the set it was handed, one retry maximum. A
failed validation, a missing type, an unpushed dependency come back as a
question in a `blocked:` line. The reply is a fixed receipt — commands
with ok/FAIL, touched paths, stderr verbatim — never a payload dump.

Knowledge still flows one way: nothing under skills/ knows the agent
exists, and deleting agents/ changes nothing.

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

.claude-plugin/marketplace.json

@@ -7,7 +7,7 @@
     {
       "name": "tea",
       "source": "./",
-      "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, 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."
     }
   ]
 }