Treat PWR_FLAG anchors as connected in orphan-wire detection

PWR_FLAG instances use a #FLG reference prefix, not #PWR, so their
pin positions were never registered as virtual connection anchors in
_parse_virtual_connections. As a result, find_orphaned_wires reported
wire ends terminating on a PWR_FLAG as dangling. Other call sites
(schematic_analysis.py:127, kicad_interface.py:3814) already recognize
#FLG as a power symbol; align this site with them.

Also coerce a previously-validated Optional[int] to int in board/layers.py
so the file passes mypy (required by the pre-commit hook); behavior is
unchanged because the value is already None-checked above.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

python/commands/board/layers.py

@@ -64,7 +64,7 @@ class BoardLayerCommands:
             # Enable inner copper layers by increasing copper layer count (KiCAD 9.0 API)
             if position == "inner":
                 current_count = self.board.GetCopperLayerCount()
-                needed_count = 2 + number  # F.Cu + B.Cu + inner layers
+                needed_count = 2 + (number or 0)  # F.Cu + B.Cu + inner layers
                 if needed_count > current_count:
                     self.board.SetCopperLayerCount(needed_count)