feat(config): default CLI_MODE to TUI

[serrrfirat]

Summary

• Changes the default CLI_MODE from empty (REPL) to "tui" so new installations get the full Ratatui terminal UI out of the box
• The tui cargo feature was already compiled in by default — this makes the runtime default match
• Users can opt out via CLI_MODE=repl in env or DB settings

Test plan

• All 12 config::channels tests pass
• All 10 config::profile tests pass
• All 114 settings tests pass
• cargo clippy --all --all-features clean
• Manual: verify cargo run launches TUI without any env vars set
• Manual: verify CLI_MODE=repl cargo run falls back to REPL

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request updates the default CLI mode to 'tui' in both the configuration settings and the channel configuration logic. A review comment suggests centralizing the default value by referencing the ChannelSettings defaults instead of hardcoding the string 'tui' in multiple places to improve maintainability and consistency.

[gemini-code-assist]

To improve maintainability and ensure consistency, consider using the default value defined in ChannelSettings instead of hardcoding the "tui" string again here. This follows the pattern used for cli_enabled and centralizes the default configuration. Additionally, use .as_ref() when accessing Option fields in structs to prevent partial moves, and prefer or_else with a closure to avoid unnecessary cloning when the first option is Some.

        let cli_mode = db_first_optional_string(&cs.cli_mode, "CLI_MODE")?
            .or_else(|| defaults.cli_mode.as_ref().cloned())
            .unwrap_or_default();

References

1. Use .as_ref().map() on Option fields within a struct to prevent partial moves, making the code more robust against future changes.