pcb-ai-engineer: reference altium_celestial_library_setup in SKILL.md

So the new Windows-setup guide is discoverable from the skill entry point.

pcb-ai-engineer/SKILL.md

@@ -222,6 +222,11 @@ In `references/` directory:
 - `mcu_db_schema.md` — MCU database schema, examples (STM32F4, ESP32-S3), blank template
 - `power_design.md` — Power supply topology guide with reference circuits
 - `review_checklists.md` — Schematic review, DRC, BOM review checklists
+- `altium_celestial_library_setup.md` — Windows setup guide for the Celestial
+  Altium Library (212k-component free DbLib): portal registration, Git LFS clone,
+  SQLNCLI11/MSOLEDBSQL driver install via direct Microsoft MSIs (no Store / no
+  winget msstore), network routing for `db.altiumlibrary.com:1433`, Altium
+  Designer configuration, full troubleshooting
 
 In `scripts/` directory:
 - `validate_mcu_db.py` — Validates mcu_db.py structure against schema