feat: port to Python and package as pip-installable distribution

Replaces main.sh with the 'cli-gnome-extension-manager' distribution in a src layout, shipping both the cli-gnome-extension-manager and the older goexma command.

sync_repository keeps the three states of the shell original apart: clone when the folder is missing, pull when it is a checkout, leave it alone otherwise, so a manually installed extension is never overwritten. build_extension still moves the checkout away before make install, but into a TemporaryDirectory instead of a fixed /tmp/<name>, which removes the collision between parallel runs and cleans up on abort.

Every step passes through the exit code of the failing tool, replacing the shell chain of || exit 1; a missing gnome-extensions aborts with exit 127. The e2e suite builds a real git repository, clones it with real git and runs real make install.

Adds --extensions-dir, unit, integration and container-based e2e tests, ruff and markdown/mermaid linting, CodeQL and Dependabot, and pins the core metadata to 2.4 so twine accepts the artifacts.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/dependabot.yml

@@ -0,0 +1,21 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+    groups:
+      actions:
+        patterns:
+          - "*"
+
+  - package-ecosystem: docker
+    directories:
+      - "/tests/e2e"
+    schedule:
+      interval: weekly
+
+  - package-ecosystem: pip
+    directory: /
+    schedule:
+      interval: weekly

.github/workflows/ci.yml

@@ -0,0 +1,80 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  test-and-lint:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: "pip"
+
+      - name: Install package and tooling
+        shell: bash
+        run: |
+          set -euo pipefail
+          python -m pip install --upgrade pip
+          python -m pip install -e .
+          python -m pip install ruff
+
+      - name: Ruff (lint)
+        shell: bash
+        run: |
+          set -euo pipefail
+          ruff check .
+
+      - name: Ruff (format check)
+        shell: bash
+        run: |
+          set -euo pipefail
+          ruff format --check .
+
+      - name: Unit tests
+        shell: bash
+        run: |
+          set -euo pipefail
+          make test-unit
+
+      - name: Integration tests
+        shell: bash
+        run: |
+          set -euo pipefail
+          make test-integration
+
+  docs:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Markdown and mermaid lint
+        shell: bash
+        run: |
+          set -euo pipefail
+          make lint-docs
+
+  e2e:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: End-to-end tests in a container
+        shell: bash
+        run: |
+          set -euo pipefail
+          make test-e2e

.github/workflows/codeql.yml

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+name: CodeQL
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: "27 4 * * 1"
+
+jobs:
+  analyze:
+    name: Check security
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+
+    permissions:
+      security-events: write
+      packages: read
+      contents: read
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: actions
+            build-mode: none
+          - language: python
+            build-mode: none
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v4
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: ${{ matrix.build-mode }}
+          queries: security-extended,security-and-quality
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v4
+        with:
+          category: "/language:${{ matrix.language }}"