feat: Dietary Vision & Consensus Interface with Gemma voice assistant

- DietaryVisionScreen.kt: Full production screen with CameraX live preview,
  bounding box overlays, classification label tags, and local action mic node
- Assistant speech bubble with Gemma LLM-generated nutritional explainer text
- 3-Frame Temporal Consensus Analysis panel with bold-highlighted pairing advice
- Quantitative Macronutrient Profile with Protein/Carbs/Fats linear bars
  and Sugar/Fiber footer grid
- Bottom navigation with floating camera+mic center hub
- Wired to real FoodVisionEngine (MediaPipe INT8) and GemmaInferenceEngine
  for on-device voice commentary generation

Author: Ashutosh0x