optimize plugin-check: round 1 — D3 fallback + D1 triggers + advisory clarification

D3: fallback when plugin-advisor.md unreachable.
D1: triggers added.
D4: explicit 'never writes' clarification (skill is advisory-only).
Size: 425B → 628B (+48%, under 150% cap).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

skills/plugin-check/SKILL.md

@@ -1,15 +1,15 @@
 ---
 name: plugin-check
-description: Audit active plugins vs project needs. Recommends enable/disable actions.
+description: Audit active plugins vs project needs. Read-only advisory recommending enable/disable. Triggers: "plugin-check", "quels plugins".
 argument-hint: [ex: "React + FastAPI" or "Rust CLI, no frontend"]
 disable-model-invocation: true
 allowed-tools: Read, Bash, Glob, Grep
 ---
 
-Load and follow strictly:
-- $HOME/.claude/agents/plugin-advisor.md
+Load and follow strictly: `$HOME/.claude/agents/plugin-advisor.md`.
 
-Analyze active plugins and the following context,
-then produce the full PLUGIN ADVISOR REPORT:
+Analyze active plugins + context below, produce PLUGIN ADVISOR REPORT.
+
+If `$HOME/.claude/agents/plugin-advisor.md` unreachable: emit `Plugin advisor agent missing.` and STOP. Never write — user toggles via `claude plugin enable/disable`.
 
 $ARGUMENTS