fix(skills): wire bump_use() into skill invocation and preload paths (#17782)

bump_use() existed and was tested but had zero production call sites —
use_count stayed 0 for all skills, breaking Curator's stale-detection
logic which relies on last_used_at.

Wire bump_use() into:
1. build_skill_invocation_message() — when a user invokes /skill-name
2. build_preloaded_skills_prompt() — when a skill is preloaded at session start

Both are the canonical 'a skill is actively being used' moments, distinct
from 'browsing' (bump_view in skill_view tool call).

Closes #17782

agent/skill_commands.py

@@ -393,6 +393,14 @@ def build_skill_invocation_message(
         return f"[Failed to load skill: {skill_info['name']}]"
 
     loaded_skill, skill_dir, skill_name = loaded
+
+    # Track active usage for Curator lifecycle management (#17782)
+    try:
+        from tools.skill_usage import bump_use
+        bump_use(skill_name)
+    except Exception:
+        pass  # Non-critical — skill invocation proceeds regardless
+
     activation_note = (
         f'[IMPORTANT: The user has invoked the "{skill_name}" skill, indicating they want '
         "you to follow its instructions. The full skill content is loaded below.]"
@@ -432,6 +440,14 @@ def build_preloaded_skills_prompt(
             continue
 
         loaded_skill, skill_dir, skill_name = loaded
+
+        # Track active usage for Curator lifecycle management (#17782)
+        try:
+            from tools.skill_usage import bump_use
+            bump_use(skill_name)
+        except Exception:
+            pass  # Non-critical
+
         activation_note = (
             f'[IMPORTANT: The user launched this CLI session with the "{skill_name}" skill '
             "preloaded. Treat its instructions as active guidance for the duration of this "