Document power symbol direct-connection behavior in tool docstrings

Power symbols at a pin coordinate create a direct electrical connection
without a wire. Note this in audit_wiring (explains wire_count: 0 for
connected pins) and add_power_symbol (explains why it draws a stub).

src/mckicad/tools/power_symbols.py

@@ -71,6 +71,11 @@ def add_power_symbol(
     name, assigns a ``#PWR`` reference, places the symbol above (supply)
     or below (ground) the pin, and draws a connecting wire stub.
 
+    KiCad's connectivity engine treats a power symbol at a pin coordinate
+    as a direct electrical connection — no wire is required.  This tool
+    places the symbol *offset* from the pin for visual clarity and draws
+    an explicit wire stub bridging the gap.
+
     This is the recommended way to connect power rails to component pins --
     it handles direction, grid alignment, and reference numbering for you.
 

src/mckicad/tools/schematic_analysis.py

@@ -1152,6 +1152,12 @@ def audit_wiring(
     ICs.  Each net entry lists which pins of the component belong to it, how
     many wire segments exist, and what other components are connected.
 
+    Note: a pin can be connected to a net with ``wire_count: 0`` when a power
+    symbol sits directly on the pin coordinate.  KiCad treats a power symbol
+    at a pin position as a direct electrical connection — no wire is needed.
+    The ``add_power_symbol`` tool draws an explicit wire stub for visual
+    clarity, but manually-placed power symbols may not have one.
+
     By default, wire segment coordinates are omitted to keep the response
     compact.  Pass ``include_wires=True`` to get full ``{start, end, uuid}``
     data for each wire (offloaded to a sidecar file when large).