Merge PR #398: feat: add SQL language support to parser

Adds .sql file parsing with dedicated _parse_sql() method:
- CREATE TABLE/VIEW -> Class nodes with extra["sql_kind"]
- CREATE FUNCTION -> Function nodes with extra["sql_kind"]="function"
- CREATE PROCEDURE -> regex fallback (grammar emits ERROR for this node)
- FROM/JOIN table references -> IMPORTS_FROM edges for impact analysis

Includes fixture (tests/fixtures/sample.sql) and TestSQLParsing tests.

Conflicts resolved:
- parser.py: kept main's newer language entries (nix, verilog, gdscript,
  expanded julia) alongside PR's SQL-specific dict entries
- test_multilang.py: kept main's TestNixParsing + TestVerilogParsing
  classes alongside PR's TestSQLParsing class

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>