refactor: split controller.go into focused files by concern

Split the 682-line controller.go into four files organized by responsibility:

- controller.go (~160 lines): types, interfaces, Controller struct, New(), Run()
- handlers.go (~170 lines): event handler registration, worker loop
- reconcile.go (~270 lines): event processing, deployment recording, caching
- pod.go (~130 lines): pod utility functions, informer factory

Extract registerEventHandlers() from New() as a Controller method and
newAPIClient() as a package-level helper to simplify the constructor.

No behavioral changes — pure structural refactoring.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bdehamer