ci: add manual OCR integration workflow

[Helio-206]

What changed

• add a manual workflow_dispatch job for the real PaddleOCR integration test;
• install the OCR service dependencies in a Python 3.11 runner;
• document the local command and the intentional separation from deterministic PR checks.

Why

The required OCR CI suite must remain deterministic and fast, while the real
PaddleOCR engine requires model downloads and is slower. This workflow makes
that integration proof reproducible on demand without making pull requests
depend on external model downloads.

Validation

• git diff --cached --check
• GitHub Actions YAML parsed locally with Ruby's YAML parser
• local full OCR execution not run: this checkout does not have pytest and
  pydantic-settings installed; the workflow installs the declared dependencies

This partially addresses #72. The issue remains open for the complete OCR test
matrix, coverage evidence, and remaining contract/integration work.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Fail the workflow when real OCR returns an error

When model download, initialization, or the actual OCR call fails, this workflow still reports success: the selected integration test calls process_image, which converts every exception into an OCRResult(status="error"), and then explicitly accepts "error" as a valid status in tests/test_engine.py:614-618. Consequently, the new manual workflow cannot provide the advertised real-engine integration proof; the test should require successful OCR output or otherwise propagate the failure.

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