build: promote tsgo to primary typechecker when TS 7.0 is GA

[goanpeca]

Phases 2-3 of #178 (TypeScript 7.x native compiler). This is the full migration: make the native compiler (tsgo / typescript@7) the authoritative typechecker and, once possible, collapse to a single compiler. It is deliberately gated and should not start until the entry conditions below are met and the parallel-job parity data from #178 Phase 1 is clean.

Entry conditions (do not start until all hold)

• TypeScript 7.0 is generally available (a stable typescript@7 / native compiler release), not a preview build.
• The Phase 1 non-blocking job has shown clean diagnostic parity with tsc@6 across recent PRs (no unexplained extra/missing errors).
• TypeDoc can build on the native compiler API, OR a decision is made to keep the JavaScript typescript solely as TypeDoc's peer dependency indefinitely.

Scope

• Promote the native compiler to the primary typecheck (replace tsc --noEmit with the native no-emit invocation).
• Update the husky pre-commit and pre-push hooks to run the native typecheck.
• Update CI so the native typecheck is the authoritative, blocking gate; remove or repurpose the Phase 1 non-blocking job.
• TypeDoc: keep pnpm docs working. Either move it onto the native compiler API (if supported) or retain the JavaScript typescript package as TypeDoc's peer dependency and document the split.
• If and only if the JS compiler is no longer needed anywhere (TypeDoc migrated), remove the transitional typescript (JS) dependency to collapse to a single compiler.
• Docs: update DEVELOPMENT.md and CONTRIBUTING.md (requirements / toolchain sections) to describe the native compiler, and add a CHANGELOG entry under [Unreleased].

Acceptance criteria

• pnpm typecheck runs the native compiler and is the authoritative gate in CI and husky hooks.
• tsc@6 (JS) is no longer the source of truth for type-checking.
• pnpm docs (TypeDoc) still builds successfully.
• The JavaScript typescript dependency is either removed (if TypeDoc no longer needs it) or explicitly retained and documented as TypeDoc's peer only.
• All existing gates stay green: pnpm all, coverage, docs:lint, docs:links, audit, and the committed-dist freshness check (ncc is unaffected, but verify).
• DEVELOPMENT.md, CONTRIBUTING.md, and CHANGELOG.md updated to reflect the new toolchain.
• The native compiler version is pinned and Dependabot-tracked.

Risks

• Diagnostic divergence on promotion could surface new type errors; the 58-file codebase keeps triage cheap.
• CI-matrix and contributor-local native-binary availability across Linux/macOS/Windows must be confirmed before this becomes a blocking gate.
• If TypeDoc parity never lands, the "single compiler" end state is deferred and this issue closes at the "native primary, JS retained for docs" milestone rather than full collapse.

Depends on

• build: evaluate and migrate typecheck to the TypeScript 7.x native compiler (tsgo) #178 (parent evaluation)
• The Phase 1 parallel-job issue (its parity report is the input to the promotion decision)