test(maturity-scoring): add unit tests for Fluency Score logic

[rajbos]

Summary

Adds 33 unit tests for maturityScoring.ts -- the module with zero test coverage that drives the AI Engineering Fluency Score, the product's core differentiating feature.

What's tested

• calculateFluencyScoreForTeamMember (all 6 scoring categories):
  • Prompt Engineering: stage thresholds at exactly 5/30/100 interactions, slash command combos, avgTurns boosters, model-switching booster
  • Context Engineering: stage thresholds at 1 ref / 3 types+10 total / 5 types+30 total, image attachment booster
  • Agentic: agent mode detection, 50-interactions + 5-non-auto-tools Stage 4 path
  • Tool Usage: zero-tools Stage 1, 2 MCP servers Stage 4, 1 MCP server stays below Stage 4
  • Customization: no-repos Stage 1, 1 customized repo Stage 2, 5+ unique models booster
  • Workflow Integration: session count thresholds, full Stage 4 combination
  • Overall median calculation: verifies all 6 category names present, all-zeros => Stage 1
• calculateMaturityScores (async personal view):
  • Stage 1 for empty stats; higher stage for active usage; all expected fields present; useCache flag forwarded correctly

Approach

All tests use plain inline object construction -- no mocks, no external dependencies.