improve: add rotation bounds and error detection to AI prompt

- Cap normal rotation to -45 to +45 degrees (flags errors beyond)
- Add explicit warning about 60°+ being measurement error
- Clarify 'safe default' is 0 if uncertain
- Prevent Gemini from wild angle guesses (like 110°)
- Help AI self-correct measurement errors

config/ai_prompt.md

@@ -90,26 +90,30 @@
     - Include minimal padding (10-15 pixels) around item edges
     - Ignore background clutter, other items, hands, reflections
 
-  ### Rotation Analysis (CRITICAL - MEASURE TEXT ANGLE)
+  ### Rotation Analysis (CRITICAL - PRECISE TEXT ANGLE MEASUREMENT)
   
-  **PRIORITY: Measure text orientation, not item orientation**
+  **IMPORTANT: Return SMALL angles (typically -45 to +45). Large angles (60°+) indicate measurement error.**
   
-  1. **Locate readable text** on the item (part numbers, manufacturer names, specifications, labels)
-  2. **Measure the baseline angle of that text**:
-     - Baseline = the invisible line the text sits on
-     - 0° = text baseline is HORIZONTAL (readable left-to-right)
-     - Positive degrees = text rotated counter-clockwise from horizontal
-     - Negative degrees = text rotated clockwise from horizontal
-  3. **Return clockwise rotation needed to make text horizontal**:
-     - If text tilted 22° counter-clockwise → return `+22` (rotate 22° clockwise to fix)
-     - If text tilted 15° clockwise → return `-15` (rotate 15° counter-clockwise to fix)
-     - If text already horizontal → return `0`
-  4. **Calibration examples** (measure the text angle precisely):
-     - Text reads perfectly left-to-right → `rotation_degrees: 0`
-     - Text tilted counter-clockwise, needs ~22° clockwise to straighten → `rotation_degrees: 22`
-     - Text vertical, pointing left (rotated 90° counter-clockwise) → `rotation_degrees: 90`
-     - Text vertical, pointing right (rotated 90° clockwise) → `rotation_degrees: -90`
-     - Text tilted clockwise by ~45° → `rotation_degrees: -45`
+  **Algorithm:**
+  1. Locate the PRIMARY text/label on the item (part number, manufacturer, specs)
+  2. Imagine a perfectly horizontal line (0°)
+  3. Measure how many degrees the text baseline is rotated FROM horizontal:
+     - Count degrees counter-clockwise = POSITIVE value to return
+     - Count degrees clockwise = NEGATIVE value to return
+     - LIMIT: Most items need -45° to +45°. If you calculate ±60° or more, re-examine your measurement.
+  
+  4. **Return exactly this value as `rotation_degrees`**
+     - SMALL adjustments: 0° to ±30° (most common)
+     - LARGE adjustments: ±31° to ±45° (rare, carefully verify)
+     - EXTREME values (±60°+): Likely error — recalculate or return 0
+  
+  **Measurement examples** (measure the TEXT BASELINE angle only):
+     - Text reads horizontally → `0`
+     - Text tilted slightly left (counter-clockwise), ~15-25° → `+15` to `+25` (NOT higher)
+     - Text tilted slightly right (clockwise), ~10-20° → `-10` to `-20` (NOT lower)
+     - Text perfectly vertical pointing left → `90` (only if TRULY vertical)
+     - Text perfectly vertical pointing right → `-90` (only if TRULY vertical)
+     - If uncertain or mixed angles → `0` (safe default)
 
   ### Confidence Score
   - Return `confidence`: 0.0-1.0 indicating reliability of crop/rotation analysis