feat(ai-logic): Add Gemini Nano Banana 2.1 quickstart

[thatfiredev]

This PR should:

• Remove the Gemini 2.5 Flash Image quickstart
• Replace the Nano Banana 2 model with Nano Banana 2.1
• Rename the Nano Banana samples so they follow the same naming pattern as "Gemini Nano Banana 2.1"

[gemini-code-assist]

Code Review

This pull request updates the Nano Banana samples by removing the deprecated Gemini 2.5 Flash Image sample, updating the model name in NanoBanana2ViewModel to gemini-nano-banana-2.1, and reorganizing the sample list. The review feedback suggests renaming the 'Nano Banana 2 Lite' and 'Nano Banana Pro' samples to 'Gemini Nano Banana 2.1 Lite' and 'Gemini Nano Banana Pro' respectively, to ensure consistent naming patterns across all samples.

[gemini-code-assist]

The PR description states that the Nano Banana samples should be renamed to follow the same naming pattern as "Gemini Nano Banana 2.1". However, this sample is named "Nano Banana 2 Lite (Gemini 3.1 Flash Image Lite)" and still references version "2" instead of "2.1". To align with the new naming pattern, it should be renamed to "Gemini Nano Banana 2.1 Lite".

Suggested change

	title = "Nano Banana 2 Lite (Gemini 3.1 Flash Image Lite)",
	description = "Generate and/or edit images using Nano Banana 2 Lite",
	title = "Gemini Nano Banana 2.1 Lite",
	description = "Generate and/or edit images using Nano Banana 2.1 Lite",

[gemini-code-assist]

To follow the same naming pattern as "Gemini Nano Banana 2.1" and maintain consistency across the samples, this sample should be renamed to "Gemini Nano Banana Pro".

Suggested change

	title = "Nano Banana Pro (Gemini 3 Pro Image)",
	description = "Generate and/or edit images using Nano Banana Pro",
	title = "Gemini Nano Banana Pro",
	description = "Generate and/or edit images using Nano Banana Pro",