fix: use correct Bitbucket API for user workspaces and clarify repo config

The `/workspaces` API endpoint was updated to `/user/workspaces` to correctly retrieve workspaces for the authenticated user.

Configuration guidance for `DEFAULT_WORKSPACE` and `DEFAULT_REPO` in documentation and templates now explicitly references deriving these values from the Bitbucket repository URL, simplifying initial setup.

.env.template

@@ -1,7 +1,8 @@
 BITBUCKET_MCP_EMAIL=your_email@example.com
 BITBUCKET_MCP_TOKEN=your_api_token
-DEFAULT_WORKSPACE=your-workspace
-DEFAULT_REPO=your-repo
+# Find these in your Bitbucket repo URL: https://bitbucket.org/my-workspace/my-repo/pull-requests
+DEFAULT_WORKSPACE=my-workspace
+DEFAULT_REPO=my-repo
 
 # Integration test write operations
 # ---------------------------------------------------------------------------------