The filters are now remembered in localStorage

Every filter, the days and title included, is stored under
job_search.filters when it changes and read back when the page loads.
A stored field that isn't valid (missing, from an older version or
edited by hand) falls back to its default, keeping the rest. Clear
filters still goes back to the defaults.

web/CODE_CONVENTIONS.md

@@ -357,8 +357,8 @@ external keep its spelling (`Authorization`, CSS `color`).
   (`readStored`, `writeStored`), which never throws: storage can be
   disabled or full, and a preference then just isn't kept.
 - Keys are listed in `STORAGE_KEYS`, prefixed with the app's name.
-- Only preferences are stored (theme, panel state); data comes from the
-  API every time.
+- Only preferences are stored (theme, panel state, filters); data comes
+  from the API every time.
 
 ## Dependencies