Summary

Establishes and enforces a consistent lifetime naming convention across the codebase:

Changes

• Parser module: 'src → 'q, 'diag → 'd
• Query module: Source<'a> → Source<'q>, QueryContext<'a> → QueryContext<'q>
• Diagnostics module: DiagnosticBuilder<'a> → DiagnosticBuilder<'d>, DiagnosticsPrinter<'a> → DiagnosticsPrinter<'q>
• Documentation: Added lifetime conventions section to AGENTS.md

Test plan

• All 720 tests pass
• cargo check passes
• cargo clippy passes