Add janitor docs/artifact spring-cleaning agent

Read-only agent that hunts stale, orphaned, and superseded
docs and artifacts and reports removal candidates with evidence.
Scope is docs/artifacts only; never deletes. Adds the guide,
the Claude wrapper, and the handbook roster + length-budget lines.

subagents-handbook.md

@@ -87,6 +87,7 @@ least one.
 | portability-checker | independence | Compliance vs my vendor-neutral / hot-swap standard | ✅ in kit |
 | exerciser | containment | Black-box QA: run it, feed it normal + hostile inputs | ✅ in kit |
 | researcher | compression | Multi-source web research → cited brief | ✅ in kit |
+| janitor | compression | Spring-clean docs/artifacts: report stale, orphaned, superseded files | ✅ in kit |
 | test-runner | compression | Run the suite, return only failures + causes | build when a repo has a real suite |
 | docs-reader | compression | Read a library's docs, return just the calls you need | build on 3rd manual-trawling task |
 | fresh-debugger | independence | Gets symptoms only (never your theories), hunts the bug | build next time you're stuck >1hr |
@@ -193,8 +194,9 @@ softened.
 
 ### Length budgets
 
-Reviewer ≤ 70 lines · exerciser, spec-checker & portability-checker ≤ 80 · researcher &
-security-auditor ≤ 100 · evaluator ≤ 120. Tighten freely; loosen only with cause.
+Reviewer ≤ 70 lines · exerciser, spec-checker, portability-checker & janitor ≤ 80 ·
+researcher & security-auditor ≤ 100 · evaluator ≤ 120. Tighten freely; loosen only with
+cause.
 
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