Reference the shared SummaryCatalog from execution plans

[zzylol]

Execution plans previously copied materialization semantics or relied on BackendPlan for cross-validation. This change makes CollectorPlan, PrecomputePlan, and TransmissionPlan reference the same authoritative SummaryCatalog snapshot by schema/version/plan identity and SHA-256 digest. Descriptor tables remain stored once in the enclosing PhysicalPlan.

PrecomputePlan now carries typed per-materialization execution contracts for update mode, placement, state schema, activation/expiry, and retained windows. validate_against_catalog verifies the snapshot reference and reconstructs expected operator, source, grouping, physical pane, encoding, placement, and lifecycle from the configured materialization. It preserves the distinction between physical pane width and query readout lookback. Collector and transmission validation reject unknown materializations, wrong plan generations, and different catalog snapshots.

This also fixes an existing compiler drift where a compatibility projection clamped a 300-second pane to 60 seconds while the state schema still advertised 300 seconds. The schema now describes the executable pane. Legacy serialized plans may omit catalog references during migration, but strict catalog-aware validation rejects them. BackendPlan remains temporarily installed until the runtime protocol migration is complete.

Validation:

• Focused PrecomputePlan catalog regression passes.
• Contributing branches passed 701 and 702 control-plane tests respectively.
• Shared SDS tests pass.

Stacked on #536.