Parser/Bridge: Unary and ASI Alignment (Stage‑2)

Context

Rust parser already parses unary minus with higher precedence (parse_unary → factor → term) but PyVM pipe path did not reflect unary when emitting MIR JSON for the PyVM harness.
Bridge（JSON v0 path）is correct for unary by transforming to 0 - expr in the Python MVP, but Rust→PyVM path uses emit_mir_json_for_harness which skipped UnaryOp.
ASI in arguments split over newlines is not yet supported in Rust (e.g., newline inside (..., ...) after a comma in a chained call), while Bridge/Selfhost cover ASI for statements and operators.

Proposed minimal steps

Unary for PyVM harness:
- Option A (preferred later): extend emit_mir_json_for_harness[_bin] to export a unop instruction and add PyVM support. Requires schema change.
- Option B (quick): legalize unary Neg to Const(0); BinOp('-', 0, v) before emitting, by inserting a synthetic temporary. This requires value id minting in emitter to remain self‑consistent, which we currently do not have. So Option B is non‑trivial without changing emitter capabilities.
- Decision: keep Bridge JSON v0 path authoritative for unary tests; avoid relying on Rust→PyVM for unary until we add a unop schema.
ASI inside call arguments (multi‑line):
- Keep as NOT SUPPORTED for Rust parser in Phase‑15. Use single‑line args in tests.
- Selfhost/Bridge side already tolerate semicolons optionally after statements; operator‑continuation is supported in Bridge MVP.

Tracking

If we want to support unary in the PyVM harness emitter:
- Add unop to tools/pyvm_runner.py and src/llvm_py/pyvm/vm.py (accept {op:"unop", kind:"neg", src: vid, dst: vid})
- Teach emitters to export UnaryOp accordingly (emit_mir_json_for_harness[_bin]).

Status

Bridge unary: OK（ny_stage2_bridge_smoke includes unary）
Rust→PyVM unary: not supported in emitter; will stay out of CI until schema update
ASI in args over newline: not supported by Rust parser; keep tests single‑line for now