chore: rename npm scope @silk-effect to @silk-lang

[julia-script]

What

Renames the npm scope from @silk-effect to @silk-lang (already owned on npm) across the whole repo: package names, workspace dependencies, imports, turbo task ids, changesets, docs, launch config, and the lockfile.

Also updated names mechanically derived from package names:

• pnpm pack tarball prefixes in release-candidate/validate.test.ts (silk-effect-* → silk-lang-*)
• the tarball path in examples/tiny-language/README.md
• the private workspace root package name (silk-effect → silk-lang)

Deliberately left as-is

• GitHub repo URLs (github.com/julia-script/silk...) — repo identity, not the npm scope
• Product-identity strings (producer: "silk-effect" in packages/llvm/src/Bitcode.ts, bootstrap shim comments, cache/tmpdir prefixes) — these are baked into binary .bc.hex golden fixtures; renaming them would churn fixtures for no packaging benefit
• packages/vscode marketplace publisher: "silk-effect" — separate marketplace identity

Notes for review

• packages/compiler-cli/src/Workflow.ts contains literal NUL bytes (committed on main), so text tools treating it as binary can silently skip it — it was patched with a binary-safe replace and verified byte-identical to HEAD apart from the scope strings.
• Verified: pnpm install clean, full turbo run build green (15/15).