Add Mistral AI OCR script with test data and documentation

- ocr.php: two-step pipeline (mistral-ocr-latest + mistral-small-latest)
  extracts Serial Number, Model Number, and Date from part label photos
- input/: 5 test images of industrial part labels
- output/: corresponding YAML results
- README.md: full usage, setup, and troubleshooting docs
- .gitignore: excludes .env only
- .env.example: API key template

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

output/WIN_20260304_15_06_20_Pro.yaml

@@ -0,0 +1,22 @@
+---
+serial_number: 2506053021331
+model_number: 38E3470018G1
+date: null
+source_file: WIN_20260304_15_06_20_Pro.jpg
+processed_at: "2026-03-04 17:26:34"
+raw_ocr: |
+  # POWER CODE
+  
+  IN-FIELD SUPPORT by VANGUARD™
+  
+  basco.com/patents • data rates apply
+  
+  Serial #:
+  2506053021331
+  
+  Model Number:
+  38E3470018G1
+  
+  ![img-0.jpeg](img-0.jpeg)
+  
+  ![img-1.jpeg](img-1.jpeg)