Let imports opt out of AI classification

Classification preferences gains "Classify newly imported transactions with
AI", stored as classify_on_import in config.toml and on by default, so existing
configurations keep their behaviour. It covers CSV imports and bank
synchronization alike.

With it off, no import path contacts the provider: classification falls to the
new provider-free rules path, where an opted-in merchant rule still applies its
category and tags, an alias match still attaches its merchant, and everything
else arrives on the editable fallback without a provenance error that would
suggest the provider had failed. Analyse remains available on demand.

web/src/main.tsx

@@ -382,7 +382,7 @@ function App() {
               )}
               {page === "settings" && (
                 <Settings
-                  key={`${state.settings.model}-${state.settings.include_amount}`}
+                  key={`${state.settings.model}-${state.settings.include_amount}-${state.settings.classify_on_import}`}
                   state={state}
                   mutate={mutate}
                 />