feat: add configurable notification retry backoff

[olalois]

Summary

• centralize retry backoff calculation across providers and retry queues
• validate retry parameters and enforce a hard maximum delay
• add configuration schema/tests and update documentation

Validation

• Editor diagnostics report no errors in changed TypeScript files
• git diff --check passes
• Jest/typecheck could not run because the container did not produce the listener dependency binaries after installation

Closes Core-Foundry#707