chore(ci): use just commands instead of direct uv/mypy calls

Refactor CI workflow to use just commands for consistency with local
development workflow. This removes the obsolete server.py exclusion
from mypy (file was removed in bcb12b4) and makes justfile's install
command accept optional extras arguments.

Changes:
- CI now uses `just install`, `just lint`, `just mypy`, `just test`
- justfile install command accepts variable extras arguments
- Removes Python 3.9 special case for server.py exclusion

Author: ryoppippi

.github/workflows/ci.yml

@@ -37,18 +37,13 @@ jobs:
         uses: ./.github/actions/setup-nix
 
       - name: Install dependencies
-        run: nix develop --command uv sync ${{ matrix.sync-extras }}
+        run: nix develop --command just install ${{ matrix.sync-extras }}
 
       - name: Run Lint
-        run: nix develop --command uv run ruff check .
+        run: nix develop --command just lint
 
       - name: Run Mypy
-        run: |
-          if [[ "${{ matrix.python-version }}" == "3.9" ]]; then
-            nix develop --command uv run mypy stackone_ai --exclude stackone_ai/server.py
-          else
-            nix develop --command uv run mypy stackone_ai
-          fi
+        run: nix develop --command just mypy
 
       - name: Run Tests
-        run: nix develop --command uv run pytest
+        run: nix develop --command just test

justfile

@@ -1,6 +1,6 @@
 # Install dependencies and pre-commit hooks
-install:
-	uv sync --all-extras
+install *extras:
+	uv sync {{ extras }}
 
 # Run ruff linting
 lint: