Clean up tools left broken or unused by asap_planner (#1161) #1186

Goal

Remove or fix what #1161 left broken or unused when asap_planner replaced stage_pipeline.

Broken

• tools/benchmark_pane_search.py reads the workload entries of tools/dag-viewer/examples.json, which One planner CLI: run stages up to a chosen point, print as JSON or text #1161 removed, and calls flags asap_planner no longer takes (--milp-time-limit-s, --cost-model). It also parses an old output format (selected/costs). It was already stale before One planner CLI: run stages up to a chosen point, print as JSON or text #1161. Fix or delete it.
• tools/validate_joint_workloads.py gives each workload a 90 s deadline. Stage 3 is now exact and unbounded, and on seed-862 workload-01 it took over 300 s, so most workloads will likely time out. Choose a deadline, or decide what this script checks now.

Unused viewer code

No current asap_planner document produces these, so they are untested end to end:

• support for archived documents (costs/selected/rejected);
• reference_pricing rows (the exhaustive search is gone);
• the memo-MILP view;
• enumeration.js and the Enumerated DAGs panel (memo.enumeration is no longer written; only hand-written fixtures cover it).

Remove them, or say why each stays.

Not reachable from the UI

tools/dag-viewer/workloads/planner-layering/example2.json is listed in neither index.json nor examples.json. Add it as a viewer tab once its Stage 3 run time is acceptable (it ran over 10 minutes in #1161's measurements), or leave it to the CLI only.