Add habit scoring logic

[AlexGladkov]

Summary

• Adds HabitScoring class with streak-based scoring and level calculation
• Contains intentional magic numbers to verify Guardian check catches violations

Guardian Check Result

6 violations detected (no_magic_numbers rule):
- val maxScore = 100
- val penaltyThreshold = 30
- days >= 365, 90, 30
- delay(5000)

Governance Context

• Proposal 2026-02-09-no_magic_numbers (add rule) — accepted, awaiting finalization
• Proposal 2026-02-09-no_hardcoded_strings (modify rule) — accepted, awaiting finalization

Test plan

• guardian check HEAD~1..HEAD detects 6 magic number violations
• guardian check HEAD~1..HEAD --json includes proposal_context in output
• Governance context section shown in human-readable output

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