fix: address PR #172 review comments

- Delete plan files per user request
- Remove KS alias per user request (keep only lowercase "knapsack")
- Fix num_slack_bits() to use integer bit-length instead of float log2
  (avoids precision loss for large i64 capacities above 2^53)
- Fix 1i64 << j to 1u64 << j in QUBO slack coefficients
  (avoids negative coefficient from signed overflow)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: zazabap