Add capability file editing

[kapelame]

Summary

• add a browser-side editor for Skill ZIP capabilities
• preserve binary files and unchanged file bytes when repacking the ZIP
• reuse the existing blob upload and capability version import/commit flow
• show the complete Skill file tree in the version viewer
• keep the implementation frontend-only, without changing parsers, database schema, import logic, bindings, or runtime

Context

This is a stacked PR based on #243 (codex/remove-capability-publish-workflow).

MCP capabilities continue to use the existing JSON/TOML editing flow. Skill capabilities download the existing ZIP, edit text files in the browser, repack the complete folder, upload it through the existing presign flow, and create a new version through the existing import commit endpoint. Skills.sh source metadata is preserved.

Validation

• pnpm --filter @parsar/web typecheck
• pnpm --filter @parsar/web build
• local end-to-end test on grill-me, creating version 1.0.1
• verified a new oss_key and SHA-256 were generated
• verified Skills.sh metadata was preserved
• verified agents/openai.yaml remained byte-identical after repacking

Targeted ESLint still reports only pre-existing findings; this change adds no new lint findings.