Update the docs after the G1–G11 consolidation groups land #677

Context

The open PRs above #577 are being consolidated into groups G1–G11:

• G1 (feat(planner): run the planning stages as the planner pipeline; retire MajorPass #674, refactor(planner): name the planner pipeline Stage 1 to Stage 3 and its fields by stage #675, merged): the planner pipeline run_stage1_to_stage3.
• G2 (refactor(planner): move Pass 1 helpers out of the legacy search; drop show_post_asap_ir, erp and empirical_comparison #676): removes the legacy replacement search, the legacy cost models and dag_export.
• G3–G11: the crate arrangement by planning stage, the Examples 1–4 work, materialization, deployment inputs, windows, and the viewer.

The user decided that these consolidation PRs do not change the Markdown docs. The docs are updated once, after the groups are done.

Docs to update after G1–G11

Many Markdown docs still describe the legacy search (MajorPass, global_selection, search_workload, the replacement strategies, dag_export, show_post_asap_ir, the legacy cost models). After the groups land they should describe the planning stages as implemented. Candidates, from the edits drafted in #676 and then reverted, and from the open docs PR #637:

• User guides: docs/user_guide_docs/run-a-query.md (global_selection, the old binaries), stage-viewer.md (once G11 rebuilds the viewer on stage_pipeline).
• Developer docs: library-api.md, asap-aware-mapping-architecture.md, asap-aware-mapping-contracts.md, extend-asap-aware-mapping.md, end-to-end-accuracy-guarantees.md, replacement-explanations.md, offline-sketch-evidence.md, physical-handoff-costs.md, storage-operation-costs.md, planner-vocabulary-migration.md, target-candidate-api-migration.md, metrics-observability-corpora.md, README.md.
• Design docs (architecture, concepts and proposals that reference the legacy search): asap-aware-mapping.md, asap-aware-plan-search.md, evidence-dependent-candidates.md, input-output-workflow.md, updated_interface_with_pluggable_optimization.md, accuracy-models.md, planner-pipeline.md, post-asap-ir.md, the asap-aware-mapping/ proposals, asapquery-rule-coverage.md, error-resource-profile.md; the decisions concat-unique-keys.md and cse-cost-model.md (links to deleted files).
• Root README.md and docs/README.md.

Conventions to follow

• Names: use the planner-layering.md stage names. Code identifiers carry the stage number and name (stage0_query_language_frontends, stage1_logical_asap_optimization, stage2_physical_asap_optimization, stage3_plan_selection; the pipeline run_stage1_to_stage3 / Stage1ToStage3Pass).
• Docs to leave alone: planner-layering.md and asap-primitive-schema.md keep their own wording, e.g. "language-specific frontends". Change them only if the user asks.
• Superseded docs: mark docs that describe removed designs as historical rather than deleting them, unless the user decides otherwise.
• Accuracy: describe actual behavior. Regenerate examples with stage_pipeline rather than writing expected numbers by hand.

Done when

No Markdown doc describes removed APIs as current, and the user guides' commands and examples run as written.

Related: #637 (open docs PR, to fold in or close), #676, #528.