dx(db): add VIX_DB environment variables with legacy ORM aliases

[GaspardKirira]

Summary

Align database configuration environment variables with the DB module name.

The DB module is separate from the ORM module, but the migration CLI still primarily uses VIX_ORM_* variables.

Current behavior

The migrator and vix orm integration use variables such as:

• VIX_ORM_HOST;
• VIX_ORM_USER;
• VIX_ORM_PASS;
• VIX_ORM_DB;
• VIX_ORM_DIR;
• VIX_ORM_TOOL.

The tool lookup already recognizes VIX_DB_TOOL, but the remaining configuration remains ORM-prefixed.

Expected behavior

New DB-specific environment variables must be supported while legacy ORM variables continue to work for backward compatibility.

Scope

• Add VIX_DB_HOST.
• Add VIX_DB_USER.
• Add VIX_DB_PASSWORD.
• Add VIX_DB_NAME.
• Add VIX_DB_MIGRATIONS_DIR.
• Standardize VIX_DB_TOOL.
• Define precedence between flags, DB variables, and legacy ORM variables.
• Update CLI help.
• Add parsing tests.
• Preserve legacy variables.

Suggested precedence

1. Explicit CLI flag.
2. VIX_DB_* variable.
3. Legacy VIX_ORM_* variable.
4. Default value.

Suggested files

• modules/cli/src/commands/OrmCommand.cpp
• modules/db/tools/migrator/MigratorCLI.cpp
• modules/db/README.md
• CLI tests.

Acceptance criteria

• New VIX_DB_* variables work.
• Legacy VIX_ORM_* variables still work.
• CLI flags override environment variables.
• DB variables override legacy ORM variables.
• Help output documents the precedence.
• Password values are not printed.
• Existing command syntax remains compatible.

Non-goals

This issue does not include:

• renaming vix orm;
• removing legacy variables;
• changing .env key names used by Config;
• ORM configuration.

Suggested labels

• scope:db
• scope:cli
• type:dx
• devx
• good first issue
• status:ready