Manage the KV cache disc usage from preferences and stats

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/schema.rs

@@ -61,6 +61,10 @@ diesel::table! {
         sidebar_collapsed -> Bool,
         last_project_id -> Nullable<Integer>,
         sidebar_width -> Integer,
+        kv_budget_gib -> Nullable<BigInt>,
+        kv_min_tokens -> Nullable<Integer>,
+        kv_cold_max_tokens -> Nullable<Integer>,
+        kv_continued_interval_tokens -> Nullable<Integer>,
     }
 }