fix(bin): put five skills' boundaries where the router can read them

grill-me, grill-with-docs, improve-codebase-architecture, tdd and triage each had
their routing boundary written into README.md, which nothing loads at runtime,
while the gate still reported all five descriptions as boundary-less. The
boundaries move into the descriptions; write-docs' clause, which said 'those have
dedicated skills' without naming one, now names them.

research had moved its body out and then read both references unconditionally --
the anti-goal ADR-0020 names, where the word count moves and the per-run context
does not. Both loads are genuinely conditional now, with the topic list and the
four literal sources.md field names inlined, since the provenance validator
matches those literally.

Also restores the promote-the-prototype anti-pattern to prototype's ui.md, which
the gate does not measure, so deleting it bought nothing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EJJrm5YmacbwMdzZpXcoti

plugins/bin/skills/tdd/SKILL.md

@@ -1,6 +1,9 @@
 ---
 name: tdd
-description: Test-driven development with red-green-refactor loop. Use when user wants to build features or fix bugs using TDD, mentions "red-green-refactor", wants integration tests, or asks for test-first development.
+description: >
+  Use when the user wants a feature built or a bug fixed test-first, in a strict
+  red-green-refactor loop, one behaviour at a time. Not diagnosing an existing
+  bug -> `diagnose`. Not throwaway exploratory code -> `prototype`.
 ---
 
 # Test-Driven Development