Rename reservations to advisory soft holds

[Jesssullivan]

Summary

• Bumps scheduling-kit to 0.8.0 for the breaking soft-hold contract rename.
• Replaces SchedulingAdapter.createReservation/releaseReservation with softHoldSlot/releaseSoftHold.
• Adds SlotSoftHold as the forward type and keeps SlotReservation as a deprecated alias.
• Updates Acuity, Homegrown, Cal.com adapters plus pipeline/test helpers to describe holds as advisory rather than authoritative reservations.

Validation

• pnpm docs:generate
• pnpm docs:generate --check
• pnpm check:release-metadata
• pnpm check
• pnpm lint
• pnpm test:unit
• pnpm test:integration
• pnpm build
• pnpm check:package
• git diff --check

Note

• pnpm docs:check could not complete in this shell because mkdocs is not on PATH; trying through nix develop was blocked by the local Nix SQLite DB lock. The generated-docs portion passed.