docs: Add Sprint 7 technical decisions documentation for US-07 macronutrient UI

documentation/Sprint7_MacroUI_Decisions.md

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+# Sprint 7: US-07 Macronutrient Information — Technical Decisions
+
+## Overview
+Sprint 7 (User Story #36 / US-07) adds personalized macronutrient target display to the LocalFoodAI interface. It is split into two focused tasks: backend data exposure (#37) and responsive UI cards (#38).
+
+---
+
+## Task #37: Backend Data Exposure
+
+### What we chose
+- **New table: `user_profiles`** (in `localfood.db`) instead of a separate `user_macro_targets` table.
+  - *Reasoning:* Avoids data duplication. The same table will be extended in a later sprint to hold full profile data (age, weight, BMR inputs). Starting with macro targets here means we have one clean place for all user personalization data.
+- **Default values** hardcoded in the schema:
+  - Calories: **2000 kcal**
+  - Protein: **150 g**
+  - Carbs: **200 g**
+  - Fat: **65 g**
+  - *Reasoning:* These are generic safe baseline values (based on general dietary guidelines). Real personalized targets will be calculated later via BMR/TDEE logic.
+- **Auto-insertion on first fetch:** The `get_user_profile()` function automatically inserts a default row if the user has no profile yet. This prevents API errors and means users always see valid values immediately on first login.
+- **Read-only endpoint:** `GET /api/macros/targets` — no POST endpoint at this stage. All data modification will be addressed when the full profile management feature is implemented.
+
+---
+
+## Task #38: Responsive Nutrient Breakdown Cards
+
+### What we chose
+- **Placement:** The dashboard is placed directly below the food search bar, above the chat, so it is always visible without scrolling.
+- **Design system:** Glassmorphism cards using `backdrop-filter: blur`, `rgba` backgrounds, and subtle borders — matching the existing chat interface design.
+- **Color coding per macro:**
+  | Macro | Color |
+  |-------|-------|
+  | Calories | Yellow `#facc15` |
+  | Protein | Red `#ef4444` |
+  | Carbs | Blue `#3b82f6` |
+  | Fat | Green `#22c55e` |
+  - *Reasoning:* Color-coded cards make it immediately clear which value is which at a glance, without needing to read the label closely.
+- **Responsive layout:** Cards use `flex-wrap` and reduce in size on screens narrower than 768px (mobile-friendly).
+- **Visibility lifecycle:** The dashboard is `display: none` by default and is only shown (`display: flex`) after a successful `GET /api/macros/targets` call at login. On logout, it is hidden again, so another user's data is never exposed.