fix: reject a session_money_budget that is not positive (#170)

[mohammadp1001]

Fixes #170.

contracts/config-schema.md says session_money_budget, if set, must be > 0. There was no validator - only stop_loss_pct had one.

A config of 0 or -500 was accepted, and then every buy failed the budget check, so the run placed no orders and looked as though the market simply never gave a signal. FR-017 exists to stop exactly that kind of silent no-op.

null stays valid and keeps meaning "no session cap". --budget 0 also still clears the cap: the CLI turns it into CLEAR before the config is built, so it never reaches this validator as 0 - test_run_budget_zero_means_no_limit covers that.

Four tests added, matching the shape of the existing stop_loss_pct ones.

598 passed in 168.10s (0:02:48)
Required test coverage of 100% reached. Total coverage: 100.00%
ruff check alphoryn/ tests/ -> All checks passed!

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (2 files)

• alphoryn/config/models.py
• tests/unit/test_config.py

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_{Reviewed by step-3.7-flash · Input: 21.6K · Output: 2.1K · Cached: 61.1K}