fix: route app.get_app_graph + ctx.*_graph to sovereign endpoints via cloud.graph_scope

[corinagum]

• App.get_app_graph(), ctx.app_graph, and ctx.user_graph were routing all Microsoft Graph calls to the public-cloud endpoint (https://graph.microsoft.com) regardless of the sovereign cloud configured on the app. Sovereign customers (GCCH, DoD, China) would hit the wrong cloud. This PR derives the Graph base URL from cloud.graph_scope on App and plumbs it through every Graph client the framework constructs.
• Public cloud (default): graph_scope = "https://graph.microsoft.com/.default" → derived base URL = https://graph.microsoft.com = previous hardcoded default. Zero behavior change.
• Sovereign clouds: behavior changes from broken (silently public) to correct (per-cloud). This is the fix.

[Copilot]

Pull request overview

Routes Microsoft Graph client construction in the Teams Apps framework to the correct sovereign cloud endpoint by deriving the Graph base URL from the configured CloudEnvironment.graph_scope and propagating it through App.get_app_graph() and ActivityContext graph properties.

Changes:

• Add a base_url override path in microsoft-teams-graph’s get_graph_client() and validate behavior via new unit tests.
• Derive Graph base URL from cloud.graph_scope in microsoft-teams-apps and pass it into all framework-created Graph clients.
• Plumb cloud through ActivityProcessor → ActivityContext so ctx.app_graph / ctx.user_graph route correctly.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/graph/src/microsoft_teams/graph/graph.py	Adds base_url override support when constructing GraphServiceClient.
packages/graph/tests/test_graph.py	Adds coverage ensuring default/public base URL and sovereign base URL routing + normalization.
packages/apps/src/microsoft_teams/apps/utils/graph.py	Derives Graph base URL from CloudEnvironment.graph_scope and forwards it to get_graph_client.
packages/apps/src/microsoft_teams/apps/routing/activity_context.py	Stores cloud on the context and uses it when creating user_graph/app_graph.
packages/apps/src/microsoft_teams/apps/app_process.py	Adds cloud to ActivityProcessor and forwards it when building ActivityContext.
packages/apps/src/microsoft_teams/apps/app.py	Passes self.cloud into create_graph_client() for get_app_graph().
packages/apps/tests/test_optional_graph_dependencies.py	Adds tests for cloud→Graph base URL derivation and updates mocks for new Graph client signature.
packages/apps/tests/test_app_process.py	Updates ActivityProcessor/ActivityContext construction to pass PUBLIC cloud.
packages/apps/tests/test_app_oauth.py	Updates ActivityProcessor/ActivityContext construction to pass PUBLIC cloud.
packages/apps/tests/test_activity_context.py	Updates ActivityContext construction to pass PUBLIC cloud.