Add configuration file support for user preferences and defaults

[solrevdev]

Description:

Implement a configuration system allowing users to set default preferences, template sources, and behavior settings.

Acceptance Criteria:

•  Support ~/.seedfolder/config.json for global settings

•  Per-directory .seedfolder.jsonconfiguration files

•  seedfolder config command group for managing settings

•  Configure default template, date prefixing, and behavior options

•  Configuration inheritance (directory > user > system defaults)

Technical Details:

• JSON-based configuration with schema validation

• Configuration loading hierarchy with proper precedence

• CLI commands for viewing and setting configuration values

• Integration with existing template selection logic

All issues build upon the completed Issue #9 foundation and can be implemented independently.

[solrevdev]

Consolidated into comprehensive Issue #15: Add External Template Sources, Configuration System, and Template Management