fix(cron): bump skill usage when cron jobs load skills

Cron jobs that reference skills via their skills: config never bumped
the usage counters in .usage.json, so the curator could auto-archive
skills actively used by cron jobs based on stale timestamps.

Now _build_job_prompt() calls bump_use(skill_name) for each
successfully loaded skill so the curator sees them as active.

cron/scheduler.py

@@ -782,6 +782,7 @@ def _build_job_prompt(job: dict, prerun_script: Optional[tuple] = None) -> str:
         return prompt
 
     from tools.skills_tool import skill_view
+    from tools.skill_usage import bump_use
 
     parts = []
     skipped: list[str] = []
@@ -793,6 +794,12 @@ def _build_job_prompt(job: dict, prerun_script: Optional[tuple] = None) -> str:
             skipped.append(skill_name)
             continue
 
+        # Bump usage so the curator sees this skill as actively used.
+        try:
+            bump_use(skill_name)
+        except Exception:
+            logger.debug("Cron job: failed to bump skill usage for '%s'", skill_name, exc_info=True)
+
         content = str(loaded.get("content") or "").strip()
         if parts:
             parts.append("")