Import Step Handler Registry

What Was Built

Replaced the repetitive string-matching dispatch in ImportSessionsController#update (5 if/return branches) and #show (4 if-branches) with frozen hash constant registries (STEP_HANDLERS and STEP_CONTEXTS). Pure refactoring with no behavior change.

Commits

• (uncommitted) refactor(controller): replace import step dispatch with handler registry

Tasks Completed

1. Add STEP_HANDLERS registry constant - Frozen hash mapping step name strings to handler method symbols for the 5 update step handlers.
2. Add STEP_CONTEXTS registry constant - Frozen hash mapping step name strings to context preparation method symbols for the 4 show step contexts.
3. Refactor update action - Replaced 5 sequential if/return branches with single registry lookup + send. Unknown steps still fall through to the default update + redirect behavior.
4. Refactor show action - Replaced 4 sequential if-branches with single registry lookup + send.
5. Verify - All 29 import_sessions_controller_test.rb tests pass. RuboCop reports 0 offenses.

Files Modified

Action	Path
MODIFY	app/controllers/source_monitor/import_sessions_controller.rb

Deviations

None. Implementation matches plan exactly.