[FIX] company: Organize company and placement listings by batch year #4

• Update company listing to display companies batch-wise.
  • Route should change from /company/ to /company/<year>/.
• Update placement listing to display students batch-wise.
  • Route should change from /company/placement/ to /company/placement/<year>/.
• Add proper handling for old routes (optional: redirect or 404).
• Update UI elements if necessary to allow selecting/viewing batches easily.

solved #28