Portable targets: newline-only lexer mode (env-spec use case)

[johnsoncodehk]

Summary

Adds newline: NewlineConfig support to the portable emit targets (TS/Go/Rust), so newline-sensitive grammars (dotenv / env-spec flavour, issue #10 lineage) can now be emitted — previously all three targets threw pattern 'never' unsupported on the engine-emitted NEWLINE token.

• IR: ParserIR.newlineCfg carries { token, flowOpen, flowClose, comment }; the never() NEWLINE token is excluded from the lexer match list (it is engine-emitted, never text-matched). Grammars declaring indent still throw (out of scope).
• Lexers (×3, symmetrical): a line-boundary state machine mirroring gen-lexer.ts newline-only semantics — exactly one NEWLINE per significant boundary, leading-boundary suppression, blank-line folding, comment-only lines skipped, flow ( … ) suspension via flowDepth.
• rd alt ordering: for newline grammars only, prefix-ambiguous rd alts are reordered longest-first at the IR level so first-match backtracking agrees with the interpreter's longest-match (e.g. Ident vs Ident '(' … ')'); the shared rdRule template is untouched.
• Gate: new test/fixtures/envspec.ts fixture + 12 cases (8 accept / 4 reject) in test/portable-targets.ts, green on all three targets.

Grammars without newline are provably unaffected: emitted calc sources at this commit are byte-identical to f6fccce for all three targets.

Validation

• node test/portable-targets.ts — envspec 8/8 + 4/4 on ts/go/rust; javascript 42/42 + 11/11, typescript 13/13 + 4/4, calc 21/21 + 7/7 baselines unchanged
• node test/check.ts emit-parity — 5/5
• node test/newline-mode.ts — 29/29 (interpreter-side regression)
• npx tsc --noEmit — clean
• Adversarial parity sweep (24 extra inputs beyond the gate: CRLF, bare CR, nested/unbalanced flow, comment/blank lines inside flow, EOF-boundary shapes) — oracle ≡ emitted TS on all

[johnsoncodehk]

Follow-up 4193aa6: planner adversarial review caught an LS/PS divergence — the executor's boundary/ws scanner treated U+2028/U+2029 as line terminators, but the interpreter's newline-only mode recognises only LF/CR (LS/PS hits the unexpected-character throw), so A=1\u2028B=2 was oracle-reject / portable-accept. All three targets now match (probe re-run: parity on all 24 adversarial inputs + 3 LS/PS witnesses; full gate, emit-parity 5/5, newline-mode 29/29, tsc, and calc byte-identity all re-verified green).