fix(L1): enforce notice for future schedule imports

[jackchuma]

Summary

• require future activations imported during initialization to satisfy MIN_NOTICE
• preserve unrestricted historical schedule imports and cover the frozen-window and exact-notice boundaries
• move proof fixtures onto a notice-compliant L2 timeline while preserving their activation-boundary assertions

Test plan

• just test (1,209 passed, 1 skipped)
• just lint-check
• just semver-lock

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1