Add comprehensive test coverage for routes and nodes

Tests cover:
- routes.py: Input validation, path traversal protection, JSON
  error handling, GUID sanitization (12 new tests)
- nodes/ideogram4_nodes.py: Prompt assembly, bbox normalization,
  palette handling, JSON serialization, input coercion (28 new tests)

All tests use mocks via conftest.py to avoid ComfyUI dependencies.
Tests import the repo as a proper package so routes.py relative
imports work unchanged.

CI: Install aiohttp for route tests.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install flake8
+        pip install flake8 aiohttp pytest pytest-asyncio
     
     - name: Lint with flake8
       run: |
@@ -43,7 +43,7 @@ jobs:
     
     - name: Run unit tests
       run: |
-        python -m unittest discover -s tests -p 'test_*.py' -v
+        python -m pytest tests/ -v
   
   javascript-check:
     runs-on: ubuntu-latest