Scenario preset editor loses unsaved edits on navigation without a prompt #4279

Describe the bug

The scenario preset editor silently discards unsaved edits when the user navigates away or refreshes. There is no route blocker and no beforeunload guard, unlike the sibling suite editor and the conversation and configuration editors, which all confirm before discarding.

Steps/Code to Reproduce

1. Open an existing preset for editing, for example /registry/scenario-presets/nightly_probe/edit.
2. Change the description, pick different techniques, or change dataset options.
3. Click any sidebar item, press browser Back, or refresh the tab.

# the guard pair exists in exactly three editors; the preset editor is not one of them
# frontend/src/components/Configuration/Configuration.tsx          useBlocker + useBeforeUnload
# frontend/src/components/Chat/ConversationEditor.tsx              useBlocker + useBeforeUnload
# frontend/src/components/ScenarioSuites/ScenarioSuiteEditor.tsx   useBlocker + useBeforeUnload
# frontend/src/components/ScenarioPresets/ScenarioPresetEditor.tsx (none)

Expected Results

A discard confirmation dialog blocks in-app navigation while edits are pending, and the browser asks for confirmation before unloading, mirroring ScenarioSuiteEditor.

Actual Results

All edits are lost immediately with no prompt, including large ones (scenario selection, parameters, datasets, techniques, name, description).

Screenshots

Not applicable.

Versions

OS: macOS
Browser: any
Python version: 3.13
PyRIT version: main at 165bdbd