Update legacy Flask handler Docker images to Python 3.13

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Required Information

• I referenced the issue addressed in this PR.
• I described the changes made and how these address the issue.
• I described how I tested these changes.

Task addressed: update the low-risk Flask handlers that still used legacy Python 3.9/3.10 Docker bases, while checking whether PyTorch-based Flask services could be safely modernized.

Changes made:

• Updated these handler images to Python 3.13: handlers/hello-svg-handler, handlers/multistage-diagram-tactile-svg, handlers/photo-tactile-svg, handlers/svg-depth-map, handlers/svg-object-detection, handlers/svg-semantic-seg, and handlers/ocr-handler.
• Replaced the old package-install steps in the Debian-based handlers with apt-get update plus explicit ca-certificates installation so pip install works reliably on current images.
• Moved handlers/ocr-handler from python:3.9.5-alpine to python:3.13-slim after validating that the Alpine variant was not building reliably in this environment.
• Left the ESPnet services unchanged because their current stacks are tied to Python 3.7-era PyTorch images, and a modern PyTorch/Python validation did not prove low-risk or buildable.

Testing performed:

• Built all seven updated handler Dockerfiles successfully with docker build from the repository root.
• Verified directly that Flask==3.1.3 does not install on the current ESPnet base images (pytorch/pytorch:1.10.0-cuda11.3-cudnn8-runtime and pytorch/pytorch:1.12.1-cuda11.3-cudnn8-runtime) because they bundle Python 3.7.
• Verified that attempting to install the current services/espnet-tts/requirements.txt on a modern PyTorch 2.7.1 / Python 3.11 image fails during dependency installation, so that modernization was not included in this low-risk PR.

Coding/Commit Requirements

• I followed applicable coding standards where appropriate (e.g., PEP8)
• I have not committed any models or other large files.

New Component Checklist (mandatory for new microservices)

• I have not added a new component in this PR.