fix(docker): add python3-tinycss2 for Inkscape DXF export

[mehulanshumali]

Description

Adds the missing python3-tinycss2 Python package to the Docker images to fix PNG → DXF conversion using Inkscape.

Problem

Inkscape's DXF export extension (dxf12_outlines.py) requires the tinycss2 module which was not installed in the container, causing PNG → DXF conversions to fail with:

** (inkscape:80): WARNING **: 13:51:34.782: Failed to wrap object of type 'GtkRecentManager'. Hint: this error is commonly caused by failing to call a library init() function.
Script Error
----
Traceback (most recent call last):
  File "/usr/share/inkscape/extensions/dxf12_outlines.py", line 29, in <module>
    import inkex
  File "/usr/share/inkscape/extensions/inkex/__init__.py", line 11, in <module>
    from .extensions import *
  File "/usr/share/inkscape/extensions/inkex/extensions.py", line 34, in <module>
    from .elements import (
    ...<10 lines>...
    )
  File "/usr/share/inkscape/extensions/inkex/elements/__init__.py", line 10, in <module>
    from ._base import ShapeElement, BaseElement
  File "/usr/share/inkscape/extensions/inkex/elements/_base.py", line 40, in <module>
    from ..styles import Style, Classes, StyleValue
  File "/usr/share/inkscape/extensions/inkex/styles.py", line 31, in <module>
    import tinycss2
ModuleNotFoundError: No module named 'tinycss2'

The error occurs because:

• Inkscape uses Python extensions for certain export formats
• The dxf12_outlines.py script imports inkex
• inkex depends on tinycss2 for CSS parsing in SVG styles

Solution

• ✅ Added python3-tinycss2 to main Dockerfile
• ✅ Added python3-tinycss2 to .devcontainer/Dockerfile for consistency
• ✅ Tested locally with Docker - PNG → DXF conversion now works

Testing Steps

1. Built Docker image locally
2. Ran container with test PDF file
3. Converted PDF → DXF using Inkscape converter
4. Verified DXF file was generated successfully without tinycss2 error

Related Issue

Fixes #494

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Summary by cubic

Added python3-tinycss2 to Docker images to fix Inkscape’s DXF export, restoring PNG → DXF conversion in the container.

• Dependencies
  • Added python3-tinycss2 to Dockerfile and .devcontainer/Dockerfile.

^{Written for commit 12e5ec3a5ca8ebc16b73b5a33b18fb83853e272e. Summary will update on new commits.}