docs: blueprint user + dev guides (Phase 8, #68)

[amaster97]

Summary

Premium-A Phase 8 documentation pass for the preflop blueprint feature
(task #68).

• New docs/blueprint_user_guide.md (~190 lines) — plain-English
  end-user explainer: what the blueprint is, what ships in the .dmg,
  when to use blueprint vs custom solve, stack-depth coverage +
  interpolation behavior, ante config selection, FAQ (Nash multiplicity
  vs published charts, blueprint vs aggregator, regeneration).
• New docs/blueprint_developer_guide.md (~370 lines) — engineering
  reference: how to regenerate blueprints (CLI flag matrix), asset +
  manifest schema, 169-class vs 1326-combo paths, True Path B engine
  internals, adding new depths or ante configs, blueprint → postflop
  subgame wiring, validation pipeline.
• README.md — new "Preflop blueprint mode" section linking both docs.
• USAGE.md §5.9 — Python API example using BlueprintLoader (Phase 2)
  and interpolate_strategy (Phase 3), plus the standard "what falls
  through to live solve" decision table.

All examples cite real shipped APIs and validation paths. PRs of
record cited: #163 (subplan), #167 (Phase 1 hybrid), #171 (True Path B
169-class kernel), #173 (interpolation), #174 (loader). Nash-
multiplicity caveat references
docs/preflop_100bb_chart_validation_v2_2026-05-28.md.

Test plan

• All cross-reference paths resolved (no broken doc links).
• Cited function names exist in source
  (BlueprintLoader.from_dir, .lookup, .actions,
  .available_depths, interpolate_strategy,
  solve_hunl_preflop_rvr_class169, Class169TerminalCache,
  build_class169_blocker_mass, _derive_continuation_ranges).
• Cited code paths exist (poker_solver/blueprint.py,
  blueprint_loader.py, blueprint_interp.py, chained.py,
  scripts/generate_preflop_blueprint.py,
  crates/cfr_core/src/preflop_rvr.rs,
  assets/preflop_equity_169x169.npz,
  tests/test_blueprint_pipeline.py).
• USAGE example compiles as valid Python syntax.
• No aspirational "future work" language; docs describe what
  actually ships post-Phase-3.
• No emojis added per memory feedback_no_extrapolate /
  task-brief rule.

Docs-only PR; auto-merge OK.

🤖 Generated with Claude Code