fix(schematic): resolve netlabel net connections to the net's ports (floating power net label)

[chayan-1906]

Fixes tscircuit/tscircuit.com#3759

Problem

A power net label connected through a net renders a phantom rail on top of an unrelated component:

<resistor name="R3" ... connections={{ pin1: "net.C", pin2: "net.CENTER" }} />
<netlabel net="V5" connection="net.C" />

The V5 rail correctly appears at R3.pin1, but a second, floating V5 rail is drawn on top of R1 (whichever component sits at schematic origin).

Root cause

NetLabel._getConnectedPorts() resolves the connection selector with selectOne(connection) and casts the result to Port. For a net selector like "net.C" this returns the Net instance, which has no schematic position, so the user's label anchors at the fallback (0, 0).

For power/ground nets the schematic trace solver then places its own rail at the real pin (getSchematicPortIdsWithAssignedNetLabels can't see that the pin already has a user-defined label, for the same reason), routes a stub trace to it, and marks the port connected — so insertNetLabelsForPortsMissingTrace never rescues the stranded user label. Result: a correct rail at R3.pin1 plus a floating duplicate at (0, 0).

Non-power labels were silently rescued by the missing-trace pass, which is why only power/ground rails visibly floated — though they still produced two identical labels stacked at the pin.

Fix

Resolve net selectors to the net's connected ports (Net.getAllConnectedPorts()) in _getConnectedPorts(). The user label then anchors at the real pin, and the existing solver logic skips both the duplicate placement (applyNetLabelPlacements) and the stub trace (applyTracesFromSolverOutput).

Before (issue repro): two V5 labels — (0.00, 0.00) on top of R1 + (-0.65, 4.36) near R3.
After: one V5 label at (-0.55, 3.96) = R3.pin1, rail_up symbol kept.
Regular labels (e.g. net="MYNET"): same position as before, no longer duplicated.

Testing

• New repro test tests/repros/repro142-floating-power-net-label.test.tsx — fails on main (phantom anchors 3.99 units away from R3.pin1), passes with the fix
• All netlabel tests pass (24 tests across 23 files)
• Full suite: 1131 pass / 28 skip; the only failure (autorouter-preset-laser-prefab) also fails on unmodified main (pre-existing)
• bunx tsc --noEmit clean, biome format clean, bun run build succeeds

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