Add uv (Astral Python package manager) support

- Add uv package manager implementation following pip pattern
- Configure MITM proxy with CA bundle for PyPI packages
- Add shell integration (bash/zsh/fish/PowerShell)
- Conditional on --include-python flag
- Add 33 comprehensive E2E tests covering:
  - uv pip install/sync/compile commands
  - uv add for project dependencies
  - uv tool install for global tools
  - uv run --with for ephemeral dependencies
  - uv sync for project syncing
  - Malware blocking verification for all methods
- Update documentation and package.json
- Install uv in Docker test environment

packages/safe-chain/src/packagemanager/uv/createUvPackageManager.js

@@ -0,0 +1,19 @@
+import { runUv } from "./runUvCommand.js";
+
+/**
+ * @returns {import("../currentPackageManager.js").PackageManager}
+ */
+export function createUvPackageManager() {
+  return {
+    /**
+     * @param {string[]} args
+     */
+    runCommand: (args) => {
+      // uv is always invoked as 'uv' - no invocation variations like pip
+      return runUv("uv", args);
+    },
+    // For uv, rely solely on MITM proxy to detect/deny downloads from PyPI.
+    isSupportedCommand: () => false,
+    getDependencyUpdatesForCommand: () => [],
+  };
+}