FT17 feat: SchemaDiffer + cli/schemaDiff.php + SchemaCompiler promote + composer schema:diff (#417)

[hideyukiMORI]

Source: FT17 (#417 / PR #418). ADR-0009 の実装本体。

やること (1 PR)

Code

• `class/xion/SchemaDiffer.php` 新規 (pure-static、DB-agnostic)
  • `diff(array $live, array $definition, string $driver): array`
  • Returns: { newTables, newColumns, warnings, inSync }
• `cli/schemaDiff.php` 新規 (PDO + stdout/stderr wrapper)
  • introspectMysql (INFORMATION_SCHEMA.COLUMNS)
  • introspectSqlite (PRAGMA table_info)
  • stdout = 適用すべき SQL のみ、stderr = annotation + warning
• `class/xion/SchemaCompiler.php` 4 helper を private → public:
  • mysqlCreateTable / sqliteCreateTable / mysqlColumn / sqliteColumn
• `composer.json` に `schema:diff` alias

Tests

`tests/Unit/Xion/SchemaDifferTest.php` 10 cases:

• in-sync / new-table (MySQL+SQLite) / new-column (MySQL+SQLite) /
  bool-default propagation / extra-column warning / extra-table warning /
  multi-warnings accumulate / inSync flag

ADR cross-link

• ADR-0009 の "Implementation tracking" section に PR # を cross-link

受け入れ条件

• composer test 138/138 (128 → 138)
• composer analyze (Phan) exit 0
• composer format:check exit 0
• live: php cli/schemaDiff.php --dsn=mysql:... で in-sync 出力
• live: DROP COLUMN 後の diff CLI が ALTER TABLE ADD COLUMN を 1 行出力
• live: DROP TABLE 後の diff CLI が CREATE TABLE 出力
• live: 追加列をした live DB に対して stderr warning + stdout 空