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

[Bartok9]

Summary

Connects bump_use() to its intended call sites so Curator's lifecycle tracking actually works.

Problem

bump_use() in tools/skill_usage.py existed and was fully tested, but had zero production call sites. As a result:

• use_count stayed at 0 for all skills
• last_used_at stayed None forever
• Curator's stale timer (30 days) couldn't distinguish used vs. unused skills
• Every non-pinned agent-created skill would transition to stale simultaneously

Meanwhile bump_view() was correctly wired into skills_tool.py.

Fix

Wire bump_use() into the two canonical "a skill is actively being used" paths in agent/skill_commands.py:

1. build_skill_invocation_message() — when a user invokes a /skill-name slash command and the skill content is injected into the prompt
2. build_preloaded_skills_prompt() — when a skill is preloaded at CLI session start via hermes --skill <name>

Both calls are wrapped in try/except to remain non-critical — skill invocation proceeds regardless of usage tracking errors.

Why these paths

• Slash command invocation = the user explicitly activated the skill to solve a task
• Preload = the user started an entire session with this skill active
• Both represent genuine "use" (vs. bump_view which tracks browsing/listing)

Testing

Existing test_skill_usage.py tests for bump_use pass. The function itself is well-tested; it simply had no callers.

Closes #17782

[teknium1]

Salvaged and merged via PR #17932 — your commit was cherry-picked onto current main with your authorship preserved in git log. Thanks @Bartok9! Widened slightly on top to also bump use_count when the agent calls the skill_view tool (the dominant skill-activation path), so curator's last_used_at signal tracks all three invocation paths: slash command, --skill preload, and skill_view tool call.