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/knowledge_dao.rs

@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 use diesel::prelude::*;
 use diesel::sqlite::SqliteConnection;
 use std::ops::DerefMut;
@@ -230,7 +232,7 @@ impl SqliteKnowledgeDao {
     }
 
     fn deserialize_embedding(bytes: &[u8]) -> Result<Vec<f32>, DbError> {
-        if bytes.len() % 4 != 0 {
+        if !bytes.len().is_multiple_of(4) {
             return Err(DbError::new(DbErrorKind::QueryError));
         }
         Ok(bytes
@@ -535,7 +537,6 @@ impl KnowledgeDao for SqliteKnowledgeDao {
 
             conn.transaction::<(i64, i64), diesel::result::Error, _>(|conn| {
                 use schema::entity_facts::dsl as ef;
-                use schema::entity_photo_links::dsl as epl;
 
                 // 1. Re-point facts where source is subject
                 let facts_updated =