chore(release): prepare v0.1.15

[chaliy]

Summary

• Bump workspace version to 0.1.15 (Cargo.toml + JS package.json)
• Add CHANGELOG.md section with 101 PRs since v0.1.14

Highlights

• Transparent request signing (bot-auth) — Ed25519 per RFC 9421 for all outbound HTTP
• Opt-in SSH/SCP/SFTP builtins — Pluggable SshHandler with russh transport, default-deny host allowlists
• Opt-in TypeScript via ZapCode — Embedded TS/JS runtime (ts, node, deno, bun builtins), VFS bridging
• AI SDK adapters — First-class JS adapters for Vercel AI SDK, OpenAI SDK, and Anthropic SDK
• Snapshot/resume — Serialize interpreter state mid-execution
• wedow/harness compatibility — Another bash compatibility milestone
• Security hardening — 20+ fixes: regex limits, memory caps, sandbox escape, credential leak prevention

Test plan

• cargo fmt --check clean
• cargo clippy --all-targets --all-features clean
• cargo test --all-features — 2,436 tests pass
• CI green on this PR
• Merge triggers release.yml → GitHub Release → publish.yml + publish-python.yml + publish-js.yml