feat: add app_level_token_rotation_enabled setting to the manifest schema

[zimeg]

Summary

This pull request adds the settings.app_level_token_rotation_enabled boolean to the v1 and v2 manifest schemas.

• Apps can opt in to rotating app-level tokens (xoxe.xapp-) with this setting
• The settings object uses additionalProperties: false, so manifests that include this field currently fail validation in editors
• Inserted alphabetically after allowed_ip_address_ranges
• Test fixtures are unchanged since tests resolve the released v0.5.0 schemas through the root router, matching feat: add code_channels feature to the manifest schema #86
• Companion CLI change: feat: add app_level_token_rotation_enabled setting to app manifest slack-cli#682

Testing

• Validate tests/manifests/v{1,2}/manifest.valid.json with "app_level_token_rotation_enabled": true added to settings against schemas/manifest.schema.{1,2}.0.0.json directly and confirm it passes
• Set the field to a non-boolean (e.g. "yes") and confirm validation fails

Category

• manifest.schema.json edit
• /schema and/or its core components
• Others

Requirements

• I've read and agree to the Code of Conduct.
• I've run ./scripts/install_all_and_run_tests.sh after making the changes.

🤖 Generated with Claude Code

[zimeg]

@WilliamBergamin Thanks for a kind review! Let's bring this out with an upcoming release so I'll merge this now.