Unify snapshot compilation under complete-cost selection

[zzylol]

Why

Snapshot startup had two selection policies: unquoted v1 compatibility compilation and complete-cost selection. Deployment should use one evidence-required path.

What / how

• Accept only snapshot schema 2. Candidate discovery can omit quotes; PromQL and MetricsQL snapshot deployment must select using valid complete workload cost evidence.
• Consolidate selected-plan output in compile_workload_artifact, including logical selection and revision metadata; remove inspect_physical_dag.
• Preserve required sketches when enumerating optional counter/max materializations, and retain whole-query native fallback for unsupported local residuals without discarding other workload summaries.
• Migrate fixtures, process tests, demo input and documentation. Synthetic quotes exist only in tests.

Before this PR

An unquoted v1 snapshot could start a backend without complete-cost selection. Mixed candidate masks could discard DDSketch bindings; missing entropy evidence could also prevent an otherwise valid L2 summary plan.

After this PR

Export candidates → measure and attach quotes → compile/select → deploy. An unquoted snapshot fails deployment explicitly. Schema version 2 is a format marker, not a second compiler mode.

Verification

• Control plane: 809 tests passed; 3 doc tests ignored.
• Experiment/calibration Python tests: 56 passed.
• Backend process suite: 12 passed; the remaining UnivMon case passed on a targeted rerun after its fix. The entire suite was not rerun after that final fix.
• CLI: unquoted candidate export succeeds, unquoted deployment fails, test-priced deployment emits a selected artifact.
• Rust formatting, shell syntax and diff checks passed.

Compatibility / limitations

This intentionally rejects schema 1 and unquoted snapshot deployment. Demo runs require ASAPQUERY_PLANNING_SNAPSHOT with valid quotes. Low-level physical binding and distributed publication APIs are outside this snapshot cleanup. Validation used Rust 1.98.0 and the CI-pinned sketchlib checkout. No new performance measurements or visual evidence apply.