refactor(planner): delete the greedy optimizer

[milindsrivastava1997]

A4 of #790. The rqe-optimizer MILP replaces the greedy optimizer, so this deletes it instead of commenting it out, which the issue originally planned. Git history keeps the old code.

Changes

• Deleted: candidate_gen, cost_model, greedy, sketch_properties, constants, translator, label_set_facts, pipeline, and the candidate-gen-dump binary (with its Cargo.toml and Dockerfile entries).
• Trimmed to what the MILP path uses:
  • atomic_costs.rs: only load_flat_atomic_cost_table and the AtomicCostEntry/AtomicCostTable re-export remain. The profile-selecting loader and resolve_atomic_costs are gone.
  • solution.rs: only OptimizerItem.
  • error.rs: only the two errors aqe_extractor returns.
  • aqe_extractor::gcd is removed (only candidate_gen used it).
• Moved: extract_hinted_items and config_to_rqes from pipeline.rs into milp.rs. MissingMetricHints and MetricsWithoutHints are now MilpError variants.
• asap-optimizer-cli is MILP-only: the --milp, --label-set-facts and --atomic-cost-workload flags are removed, and --workload-facts and --atomic-costs are plain required arguments. Nothing in the repo passed --milp.
• Removed the two greedy example YAMLs from .design_docs/. The .md design docs are unchanged.

Interface change

asap_planner::optimizer no longer exports anything greedy-related (run_greedy_pipeline, LabelSetFacts, the cost-model types). The only callers were the two binaries in this crate.

Test plan

• Ported four tests from pipeline.rs to milp.rs: metric hints required, unhinted metric rejected, spatial-only range, and group flattening.
• cargo test -p asap_planner, clippy with -D warnings, fmt; pre-commit hooks passed.
• asap-optimizer-cli --help shows the MILP-only flags.

Next: A5′ (asap-planner --planner legacy|milp), stacked on this PR.

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