fix: include KiCad 10 Windows install paths in library auto-discovery

Fixes #245 — _find_kicad_footprint_dir() only listed the 9.0/8.0 Windows
install paths, so a Windows host with only KiCad 10 installed got None and
footprint auto-discovery found nothing. The same gap existed for symbols in
library_symbol.py and dynamic_symbol_loader.py.

- Add C:/Program Files/KiCad/10.0/share/kicad/{footprints,symbols} to the
  candidate lists (10.0 first, matching the existing newest-first order)
- Honor KICAD10_FOOTPRINT_DIR and KICAD10_SYMBOL_DIR env overrides alongside
  the existing 9/8 ones
- Regression tests in tests/test_kicad10_paths.py

python/commands/library.py

@@ -182,12 +182,15 @@ class LibraryManager:
         possible_paths = [
             "/usr/share/kicad/footprints",
             "/usr/local/share/kicad/footprints",
+            "C:/Program Files/KiCad/10.0/share/kicad/footprints",
             "C:/Program Files/KiCad/9.0/share/kicad/footprints",
             "C:/Program Files/KiCad/8.0/share/kicad/footprints",
             "/Applications/KiCad/KiCad.app/Contents/SharedSupport/footprints",
         ]
 
         # Also check environment variable
+        if "KICAD10_FOOTPRINT_DIR" in os.environ:
+            possible_paths.insert(0, os.environ["KICAD10_FOOTPRINT_DIR"])
         if "KICAD9_FOOTPRINT_DIR" in os.environ:
             possible_paths.insert(0, os.environ["KICAD9_FOOTPRINT_DIR"])
         if "KICAD8_FOOTPRINT_DIR" in os.environ: