ci: add GitHub Actions, issue templates, and PR template

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,13 @@
+---
+name: Bug report
+about: Something broken
+labels: bug
+---
+
+**What happened:**
+
+**Expected:**
+
+**Steps to reproduce:**
+
+**Environment (OS, browser/version):**

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,11 @@
+---
+name: Feature request
+about: Suggest an idea
+labels: enhancement
+---
+
+**Problem / motivation:**
+
+**Proposed solution:**
+
+**Alternatives considered:**

.github/pull_request_template.md

@@ -0,0 +1,11 @@
+## What
+
+<!-- Brief description of the change -->
+
+## Why
+
+<!-- Motivation, linked issue if any -->
+
+## Test plan
+
+<!-- How was this verified? -->

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  lint-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+          cache: pip
+      - run: pip install -r requirements.txt
+      - run: pip install ruff
+      - run: ruff check src/ scripts/ --select E,F,W --ignore E501