Fix CI failures: unused Python imports and CDK synth asset path

CDK synth job needs the .NET API published first so the Lambda asset
path exists. Python lint had 3 unused imports in pdf-generate.

.github/workflows/ci.yaml

@@ -60,12 +60,16 @@ jobs:
   infra:
     name: CDK Synth
     runs-on: ubuntu-latest
-    defaults:
-      run:
-        working-directory: infra
     steps:
       - uses: actions/checkout@v6
 
+      - uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '8.0.x'
+
+      - name: Publish .NET API (required for CDK asset path)
+        run: dotnet publish api/src/ProposalSystem.Api/ProposalSystem.Api.csproj --configuration Release --runtime linux-arm64 --self-contained
+
       - uses: actions/setup-node@v4
         with:
           node-version: 24
@@ -73,4 +77,6 @@ jobs:
           cache-dependency-path: infra/package-lock.json
 
       - run: npm ci
+        working-directory: infra
       - run: npx cdk synth
+        working-directory: infra

lambdas/pdf-generate/app.py

@@ -6,17 +6,16 @@ Triggered via SQS when an admin requests PDF generation.
 
 import json
 import os
-import tempfile
 from datetime import datetime
 from io import BytesIO
 
 import boto3
 import httpx
 from reportlab.lib import colors
-from reportlab.lib.enums import TA_CENTER, TA_LEFT, TA_RIGHT
+from reportlab.lib.enums import TA_CENTER, TA_RIGHT
 from reportlab.lib.pagesizes import letter
 from reportlab.lib.styles import ParagraphStyle, getSampleStyleSheet
-from reportlab.lib.units import inch, mm
+from reportlab.lib.units import inch
 from reportlab.platypus import (
     Paragraph,
     SimpleDocTemplate,