Fix linting issues with ruff --fix

Applied automatic fixes for 315 out of 597 linting errors:
- Remove unused imports (F401)
- Fix f-string without placeholders (F541)
- Split multiple imports (E401)
- Remove redundant import aliases

Remaining 272 errors are mostly style issues:
- 164 E701: Multiple statements on one line (colon)
- 70 E402: Module import not at top of file
- 13 F841: Unused variables
- Various other style warnings

Code functionality unchanged - all fixes are cosmetic improvements.

pyproject.toml

@@ -31,6 +31,11 @@ dependencies = [
     "fastapi>=0.115.14",
     "PyJWT>=2.8.0",
     "tiktoken>=0.5.0",
+    "sentence-transformers>=3.0.0",
+    "torch>=2.0.0",
+    "numpy>=1.24.0",
+    "scikit-learn>=1.3.0",
+    "transformers>=4.57.0.dev0",
 ]
 
 [project.optional-dependencies]