Implement unified configuration system and rename data to config

[piraz]

This task establishes a standard Neovim configuration pattern for Chase, making it easier for users to customize behavior and for developers to manage defaults.

Proposed Changes:

• Rename lua/chase/data.lua to lua/chase/config.lua.
• Define a comprehensive defaults table in config.lua (covering globals, UI, and language runners).
• Update M.setup() in init.lua to use vim.tbl_deep_extend for merging user settings with defaults.
• Ensure all language runners read settings from the centralized chase.config object.

Goal:

Provide a clean API for users to enable/disable specific runners and customize execution flags without modifying the plugin's source code.