[Phase 2] syn AST rule engine and SARIF output

[ToryMic]

Description

Upgrade RytScan from line-based heuristics to a proper syn AST visitor for accurate Soroban contract analysis.

Tasks

• Add syn AST visitor for Rust contract functions
• Port AUTH-001, EVENT-001, TTL-001 to AST-based detection
• Implement SARIF v2.1.0 report serializer
• Add rytscan.toml for per-rule suppressions
• Document SARIF upload to GitHub Code Scanning

Acceptance Criteria

• Fixture scans produce same or fewer false positives vs Phase 1
• rytscan scan --format sarif validates against SARIF schema

Wave Alignment

CI security gates for Soroban PRs during Drips Stellar Wave 8 sprints.