fix: remove invalid skills frontmatter from UI agents and update test counts

Strip unsupported `skills:` key from gsd-ui-auditor, gsd-ui-checker, and
gsd-ui-researcher agent frontmatter. Update Copilot install test expectations
to 36 skills / 15 agents.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agents/gsd-ui-auditor.md

@@ -3,8 +3,6 @@ name: gsd-ui-auditor
 description: Retroactive 6-pillar visual audit of implemented frontend code. Produces scored UI-REVIEW.md. Spawned by /gsd:ui-review orchestrator.
 tools: Read, Write, Bash, Grep, Glob
 color: "#F472B6"
-skills:
-  - gsd-ui-auditor-workflow
 # hooks:
 #   PostToolUse:
 #     - matcher: "Write|Edit"

agents/gsd-ui-checker.md

@@ -3,8 +3,6 @@ name: gsd-ui-checker
 description: Validates UI-SPEC.md design contracts against 6 quality dimensions. Produces BLOCK/FLAG/PASS verdicts. Spawned by /gsd:ui-phase orchestrator.
 tools: Read, Bash, Glob, Grep
 color: "#22D3EE"
-skills:
-  - gsd-ui-checker-workflow
 ---
 
 <role>

agents/gsd-ui-researcher.md

@@ -3,8 +3,6 @@ name: gsd-ui-researcher
 description: Produces UI-SPEC.md design contract for frontend phases. Reads upstream artifacts, detects design system state, asks only unanswered questions. Spawned by /gsd:ui-phase orchestrator.
 tools: Read, Write, Bash, Grep, Glob, WebSearch, WebFetch, mcp__context7__*
 color: "#E879F9"
-skills:
-  - gsd-ui-researcher-workflow
 # hooks:
 #   PostToolUse:
 #     - matcher: "Write|Edit"