Add custom KiCad libraries for RP2040-Zero and OLED

Symbol library (SN-L00.lib/):
- RP2040-Zero: 18-pin module symbol with all GPIO labels
- OLED_128x32_I2C: 4-pin I2C display symbol

Footprint library (SN-L00.pretty/):
- RP2040-Zero: 2x9 through-hole, 15.24mm spacing, with pin labels
- OLED_128x32_I2C: 38x12mm module outline, 4-pin header

Auto-loading via fp-lib-table and sym-lib-table.

hardware/kicad/sym-lib-table

@@ -0,0 +1,4 @@
+(sym_lib_table
+  (version 7)
+  (lib (name "SN-L00")(type "KiCad")(uri "${KIPRJMOD}/SN-L00.lib/SN-L00.kicad_sym")(options "")(descr "SN-L00 project symbols"))
+)