fix(sot23): add silkscreen body outline and pin 1 marker for 3-pin variant

[rudra496]

Summary

Fixes #732.

Previously, `fp.string("sot23")` (the standard 3-pin variant) emitted no silkscreen body outline or pin 1 marker, leaving the physical component boundaries and orientation ambiguous on emitted boards.

Changes

1. Silkscreen Paths & Pin 1 Indicator: Added top and bottom silkscreen body segment paths and a triangular pin 1 marker to `sot23_3()` in `src/fn/sot23.ts`, matching sibling SOT footprints (`sot23_5`, `sot23w`, `sot323`).
2. Unit Tests: Added `tests/sot23-silkscreen.test.ts` verifying that `sot23` emits silkscreen body paths and the `pin1_indicator` path.

Verification

• `bun test tests/sot23-silkscreen.test.ts` (1/1 passing).

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