feat: Support custom keybindings via `config.toml`

[shatrughantwt]

Summary

Currently, all keybindings are hardcoded in keys.go, making it impossible for users to remap keys without modifying the source code. This request proposes moving keybinding definitions into config.toml so users can customize them freely.

Current Behavior

All key mappings are statically defined in keys.go
There is no way to override these at runtime or via configuration.

Desired Behavior

Users should be able to define custom keybindings in config.toml
If a key is not defined in config.toml, the app should fall back to the default value defined in keys.go

Proposed Implementation

• Add a [keybindings] section to the config.toml schema
• On startup, load keybindings from config and merge with defaults
• Update keys.go to read from a shared config struct instead of hardcoded values

[bakayu]

Sounds good, please go ahead and open a PR for this.
Should be a minimal change and easy one to implement, for reference see how config.toml handles user defined themes