feat: add SQL INSERT output format (-O sql)

[vmvarela]

Summary

Add -O sql output format that generates INSERT INTO statements from query results. Useful for data migration between databases, seeding databases, and creating test fixtures.

Usage

$ printf 'name,age\nAlice,30\nBob,25\n' | sql-pipe -O sql 'SELECT * FROM t'
INSERT INTO "t" ("name", "age") VALUES ('Alice', 30);
INSERT INTO "t" ("name", "age") VALUES ('Bob', 25);

$ printf 'name\nO'"'"'Brien\n' | sql-pipe -O sql --sql-table users 'SELECT * FROM t'
INSERT INTO "users" ("name") VALUES ('O''Brien');

Changes

File	Change
src/format.zig	OutputFormat.sql, WriteOpts.sql_table, writeSqlRow() + writeSqlId/writeSqlStringLiteral helpers
src/args.zig	ParsedArgs.sql_table, --sql-table flag, updated help text
src/main.zig	sql_table wired through execQuery to OutputWriter
build.zig	9 integration tests
README.md	-O sql and --sql-table documented
docs/sql-pipe.1.scd	Man page updated

Value formatting

• NULL → NULL (unquoted)
• INTEGER → raw decimal (42, -7)
• FLOAT → raw, trunc check (30.0 → 30, 3.14 → 3.14)
• TEXT → single-quoted with '' escaping
• Identifiers double-quoted with "" escaping

Testing

• zig build test — all pass (9 new SQL output tests)
• zig build unit-test — all pass
• Oracle plan review and final review both approved

Closes #174