chore: open-source dev environment and release automation (issue #6)

[bitIO]

Summary

Open-source readiness for this plugin: Biome linting, husky + commitlint for conventional commits, semantic-release-based real npm publishing for @bitio/opencode-provider-balance, CI hardening, README banner/badges/troubleshooting, docs/, SECURITY.md + issue/PR templates, LICENSE/Code of Conduct/CONTRIBUTING, and a committed bun.lock.

What changed

• Tooling: add Biome linter and apply formatting fixes
• Conventions: husky hooks + commitlint enforcing conventional commits
• Release: semantic-release dry-run configuration; enable real releases with npm publishing (prod environment)
• CI: run lint in CI workflow; harden workflow with audit and pack checks; run release job in prod environment
• Docs: README banner, badges, troubleshooting; docs/ folder; security policy and issue/PR templates
• Legal/community: contributing guide, code of conduct, license
• Chore: commit bun.lock for reproducible installs; rename package to @bitio/opencode-provider-balance

Verification

• Lint, typecheck, 47 tests, and build all green
• commitlint enforces conventional commits on push
• semantic-release dry-run computes version 1.0.0
• npm pack --dry-run verified
• CI and release workflows validated

Decisions

• Package renamed to @bitio/opencode-provider-balance because the unscoped name is taken on npm
• Real publishing enabled per human approval
• Releases trigger on merge to main via the prod environment

Review notes

• SECURITY.md fallback email opensource@bitio.dev is a placeholder to confirm
• assets/banner.png source kept alongside the webp

Closes #6