docs: add Tier 3 ILP reduction paper entries, design spec, and implementation plan

- 39 new reduction-rule entries in reductions.typ with standardized
  multiline ILP equation blocks (variables, constraints, objective)
- Expanded 9 complex entries with full variable indexing, big-M values,
  and flow schemes (MixedChinesePostman, StackerCrane, AcyclicPartition,
  BiconnectivityAugmentation, BoundedComponentSpanningForest,
  StrongConnectivityAugmentation, ConsecutiveOnesMatrixAugmentation,
  StringToStringCorrection, RootedTreeStorageAssignment)
- Added equation blocks to all existing Tier 1/2 ILP entries
- Fixed ShortestWeightConstrainedPath MTZ constraint inversion
- Fixed 10 undefined/mismatched symbols across entries
- Standardized ILP problem-def with multiline equation
- Design spec: docs/superpowers/specs/2026-03-24-tier3-ilp-reductions-design.md
- Implementation plan: docs/superpowers/plans/2026-03-24-tier3-ilp-reductions.md

2 problems deferred: PartialFeedbackEdgeSet (no poly-size ILP for L<n),
RootedTreeArrangement (compound vec![n;2*n] config).

Ref #762.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: GiggleLiu