fix(examples): wire board-less button power via 2.l so the pushbutton enters SPICE

The pushbutton SPICE mapper reads pins '1.l' and '2.l', but killbits/counter
wired the power side to '2.r' (an un-unioned sub-pin), so netLookup('2.l')
returned null and the button was omitted from the netlist entirely — pressing
did nothing electrically board-less. Wire the power side via '2.l' so the
button becomes a real (pressed -> 0.01 ohm) bridge to VCC, which the pull-down
+ connectChipInputsToSolve then turn into a HIGH the chip reads.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/data/examples-retro-intel.ts

@@ -392,13 +392,13 @@ export const retroIntelExamples: ExampleProject[] = [
       },
       {
         id: 'wire-btn-inc-pwr',
-        start: { componentId: 'btn-inc', pinName: '2.r' },
+        start: { componentId: 'btn-inc', pinName: '2.l' },
         end: { componentId: 'psu', pinName: 'SIG' },
         color: '#e74c3c',
       },
       {
         id: 'wire-btn-rst-pwr',
-        start: { componentId: 'btn-rst', pinName: '2.r' },
+        start: { componentId: 'btn-rst', pinName: '2.l' },
         end: { componentId: 'psu', pinName: 'SIG' },
         color: '#e74c3c',
       },
@@ -536,7 +536,7 @@ export const retroIntelExamples: ExampleProject[] = [
       })),
       ...[0, 1, 2, 3, 4, 5, 6, 7].map((i) => ({
         id: `wire-btn-${i}-pwr`,
-        start: { componentId: `btn-${i}`, pinName: '2.r' },
+        start: { componentId: `btn-${i}`, pinName: '2.l' },
         end: { componentId: 'psu', pinName: 'SIG' },
         color: '#e74c3c',
       })),