feat(events): add public all-events collection

[wilber123451-design]

Summary

• add a backend-only virtual all-events collection populated from deployed Unlock events with checkout configs
• strip protected event attributes and reserve the virtual slug from user-created collections
• make the collection read-only in the UI and add an Explore events entry point from the events landing page
• expose the virtual flag in the Locksmith OpenAPI schema

Fixes #16183

Verification

• yarn workspace @unlock-protocol/locksmith vitest run __tests__/operations/eventCollectionOperations.test.ts (21 tests passed)
• targeted Locksmith and unlock-app ESLint (no errors)
• yarn workspace @unlock-protocol/unlock-app tsc --noEmit
• yarn workspace @unlock-protocol/unlock-js generate:locksmith

Bounty payout

Please confirm the Scout Game Gold reward for this implementation. If accepted, the Base USDC payout address is 0xd3CE8223E6b0F446a887953aF623B9c72233Ba39.

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