feat(fusion_accounting_ocr): pluggable OCR for vendor bills

Replaces Enterprise's account_invoice_extract with a Fusion-native pipeline:

Stage 1 (text extraction): Tesseract OCRs the bill attachment via
pytesseract + pdf2image. Pluggable OCRProvider adapter pattern allows
future Mindee / Google Document AI / Ollama-vision backends.

Stage 2 (field parsing): The fusion_accounting_ai LLMProvider reads the
raw OCR text and returns structured invoice fields (vendor, invoice
number, dates, amounts, line items) as JSON.

Draft invoice fields are auto-populated for empty-only fields (never
overwriting user-entered data). Vendor matching by name against
res.partner with supplier_rank > 0.

Adds:
- account.move.ocr_state (selection: not_requested/pending/processing/
  done/failed/manual)
- account.move.ocr_raw_text, ocr_extracted_data (Json), ocr_backend,
  ocr_confidence
- fusion.ocr.log (audit trail per OCR run)
- res.company.fusion_ocr_enabled / fusion_ocr_default_backend / auto_run
- /fusion/ocr/request_for_invoice JSON-RPC endpoint

Backend availability detected at runtime via OCRProvider.is_available()
classmethods. Tesseract 5.3.4 + pytesseract 0.3.13 + pdf2image 1.17.0
are installed in the container.

Tests: 13 (TesseractAdapter availability + image OCR; flow tests for
draft autofill, no-attachment guard, customer-invoice guard, ref-not-
overwritten; field parser empty/clean-json/markdown-fence/bad-JSON/
provider-exception). All pass on westin-v19 OrbStack VM.

Made-with: Cursor

fusion_accounting_ocr/services/ocr_providers/manual_adapter.py

@@ -0,0 +1,13 @@
+"""Manual fallback adapter - no real OCR, just marks the document as
+'awaiting manual entry'. Used when no real OCR backend is available
+or when the user explicitly disables OCR.
+"""
+
+from .base import OCRProvider, OCRResult
+
+
+class ManualAdapter(OCRProvider):
+    name = 'manual'
+
+    def extract(self, image_or_pdf_bytes, *, mimetype='application/pdf'):
+        return OCRResult(raw_text='', confidence=0.0, pages=0, backend='manual')