CI-03: Replace logging f-strings with % or .format() (G004)

[longieirl]

Context

Phase 25 (Ruff Migration, issue #89) enabled the G ruleset. 214 G004 violations exist across the codebase — all are f-strings inside logging calls.

Approach

Use ruff's AST-transform auto-fix (available in ruff >=0.4.0) or manual replacement. Before: logger.info(f"Processing {filename}"). After: logger.info("Processing %s", filename)

Scope

• 214 violations across parser-core and parser-free
• All are logger.info/debug/warning/error(f"...") patterns
• Auto-fixable with careful review (format specifiers may differ)

Acceptance criteria

• ruff check --select G004 exits 0
• G004 removed from lint.ignore in both pyproject.toml files

Related: #89 (Ruff Migration)