chore: apply cargo fmt + clippy cleanup across crate

Silence forward-looking dead_code on unused DAO modules, annotate
individual placeholder items, rewrite tautological assert!(true/false)
in token tests as panic! arms, and pick up fmt drift.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/database/daily_summary_dao.rs

@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 use chrono::NaiveDate;
 use diesel::prelude::*;
 use diesel::sqlite::SqliteConnection;