chore(release): 0.5.0

[tt-a1i]

Summary

• bump @tt-a1i/openpi from 0.4.0 to 0.5.0
• release the Pi-native OpenPI Web Workbench and interactive /web launcher
• include the accumulated Session, Subagent, Workflow, TUI, setup, safety, performance, and repository-governance improvements on current main
• preserve the existing standalone openpi web <workspace> CLI contract while /web starts an independent browser-owned workspace

This is a minor release because the public feature surface has expanded since 0.4.0; it is not only a patch set.

Release gates

• current main CI at 51b85ad: passed
• bun run check: passed
• bun run test: 1235 Node tests passed, 1 skipped; 30 Vitest tests passed
• npm pack --dry-run --json --ignore-scripts: @tt-a1i/openpi@0.5.0, 176 files, 686,335 bytes compressed, 2,049,622 bytes unpacked
• git diff --check: passed

Publication plan

After merge, create v0.5.0 at the exact merged main commit. The tag-triggered Release workflow will re-run validation, build a single npm artifact, and publish it through the protected npm environment with OIDC. Publication is not complete until the workflow, npm dist-tag/provenance, GitHub Release, and clean install smoke are verified.