Multiple playgrounds - batch installation and token/webhook rotation

Problem

We manage ~50 playground projects that require the same CLA-Bot setup. Installing the bot and rotating tokens/webhooks manually for each project is impractical and error-prone.

Proposal

Extend install-bot with a batch mode driven by a manifest file (stored in the home repository). The installer should accept a single PAT at runtime and perform idempotent create/update actions for tokens, CI variables, and webhooks across all listed playgrounds.

Suggested manifest fields:

• instance_url
• home_project
• store_project
• storage_scope (instance | group | project)
• playground_projects (when storage_scope = project)
• playground_groups (when storage_scope = group)
• storage_type, cla_store_branch, etc.

Impact

Scales installation and token rotation to dozens of projects, reduces manual effort and operational risk.

Related to #28 (moved)