feat: Add property-based testing with Hypothesis

[mark-e-deyoung]

Description

Add property-based/fuzz testing using the Hypothesis library for core operations (store, audit log, planner).

Why

Example-based tests miss edge cases. Property-based testing systematically explores input space to find latent bugs.

Status

Deferred — Python codebase is small (~1000 lines) and mostly orchestrates Docker commands. Revisit when:

• Core logic is significantly extended
• A bug is found that property-based testing would have caught
• The store/audit SQLite operations need higher assurance

References

• Hypothesis: https://hypothesis.readthedocs.io/
• Item L from testing audit (2026-07-05)