MySkills

## Changed

**Datapack-Driven Skill Tuning**
Skill cost and cooldown can now be overridden per-skill via datapacks, without needing a mod update:
- Drop a JSON file at `data/<namespace>/skill_tuning/<skill_id>.json` with `"cost"` and/or `"cooldown_ms"` — either field is optional, and anything you don't specify falls back to the built-in default
- Changes apply on `/reload`, no restart required
- Note: cost is keyed by the specific skill ID (e.g. `wind_slash_1`), while cooldown is keyed by the shared action ID used across that skill's tiers (e.g. `wind_slash`) — these can live in separate files if needed
- The cooldown overlay now stays in sync with server-side overrides automatically

## Fixed

- **Keybind conflicts** no longer trigger against skills you haven't unlocked yet. Previously, a stale key binding left over from a skill you unlocked in another world/session could block you from assigning that key elsewhere, even though the conflicting skill wasn't visible or accessible.
- **Cooldown display** was silently missing for most tiered skills (e.g. Wind Slash, Earth Slam, Thunder Strike, Cross Slash) — the on-screen cooldown bar simply wouldn't appear for them, even though the cooldown itself was correctly enforced. Now shows correctly for all skills.