Add DMT6007LFG-7, TPS2121RUXR, Lattice ECP5 FPGA symbols; fix quoted 3D model path check

- Add DMT6007LFG-7 (transistor) and TPS2121RUXR (dual-input power mux) with
  footprints and TPS2121RUXR's 3D model.
- Import Lattice_ECP_FPGA symbol library (ECP5U-45 CABGA256/381/554,
  CSFBGA285) from mattvenn/basic-ecp5-pcb's legacy .lib, converted via
  kicad-cli sym upgrade; symbol-only, footprints resolved via the standard
  Package_BGA KiCad library. Add a vendor-accurate BG256 3D body
  (LFE5U-25F-8BG256I) for manual per-instance assignment.
- Fix check_library.py's 3D model reference regex to strip surrounding
  quotes, which KiCad 10's re-save format adds around (model "...") paths
  -- was causing a false "missing 3D model" error for SJ-3506-SMT-TR after
  its footprint got re-saved in the new format.

scripts/check_library.py

@@ -219,8 +219,8 @@ def check_footprints(report: Report) -> dict[str, Path]:
             key = f"{nickname}:{mod.stem}"
             footprint_owner[key] = mod
 
-            for model_m in re.finditer(r'\(model\s+([^\s)]+)', text):
-                model_ref = model_m.group(1)
+            for model_m in re.finditer(r'\(model\s+"([^"]+)"|\(model\s+([^\s)]+)', text):
+                model_ref = model_m.group(1) or model_m.group(2)
                 check_model_reference(report, mod, model_ref)
 
     for digest, paths in seen_hash.items():