Drop requirements.txt; run lint via uv

The integration's runtime deps come from manifest.json; requirements.txt
was only consumed by the lint workflow and had drifted from pyproject.toml.
Switch the Ruff job to setup-uv + `uv run ruff`, sourcing the pinned ruff
from pyproject.toml/uv.lock, and remove the redundant requirements.txt.

Author: bkanuka

.github/workflows/lint.yml

@@ -18,17 +18,13 @@ jobs:
       - name: Checkout the repository
         uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
 
-      - name: Set up Python
-        uses: actions/setup-python@83679a892e2d95755f2dac6acb0bfd1e9ac5d548 # v6.1.0
+      - name: Set up uv
+        uses: astral-sh/setup-uv@d0cc045d04ccac9d8b7881df0226f9e82c39688e # v6.8.0
         with:
-          python-version: "3.13"
-          cache: "pip"
-
-      - name: Install requirements
-        run: python3 -m pip install -r requirements.txt
+          enable-cache: true
 
       - name: Lint
-        run: python3 -m ruff check .
+        run: uv run ruff check .
 
       - name: Format
-        run: python3 -m ruff format . --check
+        run: uv run ruff format . --check