Cleanup IMPORT_BRUSH Intent

[maxmmitchell]

• Avoid navigating to brush graph when we're already there for a smoother experience. When we try to "re-navigate" to the same screen we're already on, there's a flash of white on the screen and it feels a bit "glitchy".
• Go to brush graph even if the brush fails to be imported, to confuse the user less on import failures (if user is expecting Cahier to launch, brush graph to launch, and their brush to be loaded, we should do as many of those as we can to make it clear which part of the chain broke).
• Use Toast to signal import intent status as well as postDebug, since the debug messages tend to get lost if the import happens along with loading up the app (debug is posted before brush graph is loaded, and so is not visible once brush graph is loaded into; but a Toast is).
• Animate notification icon on change in issues to draw attention to status updates.

[gemini-code-assist]

Code Review

This pull request modifies the brush import flow by triggering navigation to the brush graph before the import operation begins and adding a safety check in CahierApp.kt to prevent redundant navigation. The reviewer correctly pointed out that navigating before the import completes or if it fails can lead to an inconsistent UI state, and suggested reverting this change to ensure navigation only occurs upon a successful import.

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