fix: resolve pre-existing CI failures (clippy, fmt, test)

[Marenz]

Fixes 17 pre-existing clippy errors, a failing test, and a broken integration test that were blocking CI on main and on any PR branching from it.

Clippy (collapsible-if, question-mark, too-many-arguments, items-after-test-module):

• Collapse nested if blocks using let-chains (stable since Rust 1.88 / edition 2024)
• Use ? instead of let Some(x) = y else { return None } in config.rs
• Add #[allow(clippy::too_many_arguments)] on TwitchAdapter::new
• Move mod tests to end of cron/scheduler.rs to fix items_after_test_module

Test fix (messaging::telegram::tests::bold_and_italic_nested):
Add a BOLD_ITALIC_PATTERN for ***text*** processed before the bold/italic patterns, so triple-star produces correct <b><i>text</i></b> nesting instead of <b><i>text</b></i>.

Integration test fix (tests/context_dump.rs):
SkillSet::render_channel_prompt returns Result<String> but the test was using it as String. Add .unwrap_or_default().

[Marenz]

@jamiepine I would suggest we enable the "must pass CI for merging PR" setting to avoid having to fix this over and over :)

[jamiepine]

Great idea, will enable that now! I also invited you as a collaborator to the repo, your contributions have been awesome, you're the top contributor.

Would also be great to have a line of communication without outside of GitHub, so if you want please email jamie@spacedrive.com