Added args, kwargs search - #20

Add a second search field on the tasks page to look for text inside a
task's args and kwargs. It works alongside the existing name search.

API / backend:

• New argsSearch query param on GET /api/tasks (zod schema, QueryParams type)
• TasksRepository.getAll accepts args and filters by substring over
  args || ' ' || kwargs:
  • postgres: lower(...) LIKE, backed by a new optional gin_trgm index
    idx_taskiq_admin_tasks__args_trgm (needs pg_trgm, warns if missing)
  • sqlite: LIKE ... ESCAPE '' (case-insensitive for ASCII only)
• User input is escaped, so % and _ are matched literally

Name search fixes:

• postgres: use lower(name) LIKE, so the existing gin_trgm index is used
• sqlite: queries shorter than 3 characters fall back to LIKE, because
  the FTS5 trigram tokenizer cannot match them

UI (tasks/index.vue):

• New "Search args / kwargs..." input; Enter submits both fields
• Search inputs are filled from the URL query on load
• Submitting resets to page 1 and clears empty fields
  (before, an empty search could not be cleared)
• "Clear Filters" also clears both inputs