refactor: rename operate to browser

[jackwener]

Summary

• rename the built-in browser control command from opencli operate to opencli browser
• rename the bundled skill from opencli-operate to opencli-browser and update related generate/autofix/usage docs
• keep inspect-with-browser in GenerateOutcome while leaving the existing schema version at 1, matching the decision that this contract is still too new to treat as a published external version boundary
• keep only the existing extension-side workspace-prefix bridge for operate: -> browser: sessions; do not keep CLI or skill compatibility shims

Verification

• npm run typecheck
• npx vitest run src/generate-verified.test.ts src/skill-generate.test.ts src/cli.test.ts --project unit --reporter=verbose
• npm run build
• node dist/src/main.js browser --help