refactor: rotation analysis to handle any photo angle

Real-world photos come at ANY angle - upside down, sideways, at weird
tilts. Stop assuming small angles. Instead:

- Measure CURRENT text orientation (horizontal/vertical/upside-down/tilted)
- Calculate rotation needed to make it READABLE in standard English
- Allow full -180° to +180° range
- No artificial limits or assumptions about how operator took the photo

Examples: vertical text → ±90°, upside-down → ±180°, tilted → measure tilt

This gives Gemini freedom to analyze real-world messy photos correctly.

config/ai_prompt.md

@@ -90,30 +90,32 @@
     - Include minimal padding (10-15 pixels) around item edges
     - Ignore background clutter, other items, hands, reflections
 
-  ### Rotation Analysis (CRITICAL - SMALL TILT ANGLE MEASUREMENT)
+  ### Rotation Analysis (CRITICAL - MAKE TEXT READABLE IN STANDARD ENGLISH)
   
-  **IMPORTANT: The image has EXIF orientation metadata stripped. Analyze it in its RAW/NATIVE state.**
+  **IMPORTANT: Photos may be at ANY angle. Your job: return the rotation angle to make the TEXT readable in standard English (horizontal, left-to-right, top-to-bottom).**
   
-  **Return the SMALL tilt angle needed to make the text perfectly horizontal and readable.**
+  **The image has EXIF orientation metadata stripped. Analyze it in its RAW/NATIVE state. Measure how much to rotate the image so that the PRIMARY label text reads normally.**
   
   **Algorithm:**
   1. Locate the PRIMARY text/label on the item (part number, manufacturer, specs)
-  2. **Measure ONLY the tilt angle**: How many degrees is the text rotated from horizontal?
-     - Text reads horizontally left-to-right → `0°`
-     - Text tilted slightly clockwise (right side up) → **negative angle** (e.g., `-15°`)
-     - Text tilted slightly counter-clockwise (left side up) → **positive angle** (e.g., `+20°`)
-  3. **IGNORE text orientation** (vertical/sideways): The image is in raw/native state, so text orientation is simply directional tilt, not a 90° shift
-  4. **Return this tilt angle as `rotation_degrees`** (expected range: **-45° to +45°**)
-     - Clockwise tilt = NEGATIVE value (e.g., `-22°` to level a clockwise tilt)
-     - Counter-clockwise tilt = POSITIVE value (e.g., `+18°` to level a counter-clockwise tilt)
+  2. Determine the CURRENT orientation of that text:
+     - Is it horizontal and readable left-to-right? → rotation needed: `0°`
+     - Is it rotated 90° (vertical, pointing up)? → rotation to horizontal: `-90°` or `+90°` (depending on which way)
+     - Is it rotated 180° (upside down)? → rotation to horizontal: `±180°`
+     - Is it tilted at an angle? → measure exact tilt needed to make it horizontal
+  3. **Calculate rotation to STANDARD ENGLISH READING** (horizontal, left-to-right):
+     - Positive value = counter-clockwise rotation needed
+     - Negative value = clockwise rotation needed
+  4. **Return any value in range -180° to +180°** (full circle allowed)
   
-  **Measurement examples** (RAW image, EXIF-stripped, measuring ONLY tilt):
-     - Text reads perfectly horizontal → `0`
-     - Item tilted 22° clockwise (text tilts down-right) → `-22`
-     - Item tilted 15° counter-clockwise (text tilts up-left) → `+15`
-     - Item slightly rotated 5° → `-5` or `+5` depending on direction
-     - **SAFETY CHECK**: If your calculated angle is > ±45°, re-examine. Most hardware is only slightly tilted in photos (±30° max)
-     - If uncertain → `0` (safe default; OpenCV fallback will handle it)
+  **Measurement examples** (make text readable left-to-right, top-to-bottom):
+     - Text already reads normally horizontally → `0°`
+     - Text is vertical, pointing up (90° rotated) → `-90°` (rotate clockwise to make horizontal)
+     - Text is vertical, pointing down (270° rotated) → `+90°` (rotate counter-clockwise)
+     - Text is upside-down (180° rotated) → `+180°` or `-180°` (rotate half-circle)
+     - Text at 22° angle (tilted right) → `-22°` (rotate clockwise to level)
+     - Text at -35° angle (tilted left) → `+35°` (rotate counter-clockwise to level)
+     - **No angle limit**: Photos may be taken at any angle. Return whatever rotation makes the label text readable in standard English orientation.
 
   ### Confidence Score
   - Return `confidence`: 0.0-1.0 indicating reliability of crop/rotation analysis