fix: make skill loading instructions more aggressive in system prompt (#8286)

The previous wording ('If one clearly matches') set too high a threshold,
and 'If none match, proceed normally' was an easy escape hatch for lazy
models. Now:

- Lowered threshold: 'matches or is even partially relevant'
- Added MUST directive and 'err on the side of loading' guidance
- Replaced permissive closer with 'only proceed without if genuinely none
  are relevant'

This should reduce cases where the agent skips loading relevant skills
unless explicitly forced.

agent/prompt_builder.py

@@ -762,7 +762,10 @@ def build_skills_system_prompt(
             "than to miss critical steps, pitfalls, or established workflows. "
             "Skills contain specialized knowledge — API endpoints, tool-specific commands, "
             "and proven workflows that outperform general-purpose approaches. Load the skill "
-            "even if you think you could handle the task with basic tools like web_search or terminal.\n"
+            "even if you think you could handle the task with basic tools like web_search or terminal. "
+            "Skills also encode the user's preferred approach, conventions, and quality standards "
+            "for tasks like code review, planning, and testing — load them even for tasks you "
+            "already know how to do, because the skill defines how it should be done here.\n"
             "If a skill has issues, fix it with skill_manage(action='patch').\n"
             "After difficult/iterative tasks, offer to save as a skill. "
             "If a skill you loaded was missing steps, had wrong commands, or needed "