ci: add flake8 lint workflow; fix unused imports and f-string issues

Adds .gitea/workflows/lint.yml running flake8 with .flake8 config.
Removes unused sys/urllib.request imports (F401).
Removes f prefix from 52 f-strings that had no placeholders (F541).
Auto-fixes trailing whitespace in blank lines (W293) via autopep8.
Fixes over-indentation in LXC storage check try block (E117).
Config ignores F841 (unused locals) and E501 (long lines).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.flake8

@@ -0,0 +1,6 @@
+[flake8]
+max-line-length = 120
+# F841: local variable assigned but never used — many are intentional debug/future-use assignments
+# E501: line too long — URLs and log messages in monitoring code are exempt
+extend-ignore = F841, E501
+exclude = __pycache__, .git

.gitea/workflows/lint.yml

@@ -0,0 +1,20 @@
+name: Lint
+
+on:
+  push:
+    branches: ["**"]
+  pull_request:
+    branches: ["**"]
+
+jobs:
+  python-lint:
+    name: Python (flake8)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install flake8
+        run: pip install flake8
+
+      - name: Run flake8
+        run: flake8 .