refactor: change OAuth scope separator from colon to dot for IDP compatibility

Many identity providers (AWS Cognito, Okta, Azure AD) reject or mishandle
colons in OAuth scope names. This migrates all custom scopes from
`resource:action` to `resource.action` format (e.g., `notes:read` →
`notes.read`), which is universally accepted and aligns with industry
conventions (Microsoft, Google).

Includes Alembic migration 004 for stored scope strings and ADR-024
documenting the rationale and RFC references.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_cli.py

@@ -251,15 +251,15 @@ def test_default_values(runner, clean_env, monkeypatch):
     # Verify default values
     assert captured_env["NEXTCLOUD_OIDC_SCOPES"] == (
         "openid profile email "
-        "notes:read notes:write "
-        "calendar:read calendar:write "
-        "todo:read todo:write "
-        "contacts:read contacts:write "
-        "cookbook:read cookbook:write "
-        "deck:read deck:write "
-        "tables:read tables:write "
-        "files:read files:write "
-        "sharing:read sharing:write"
+        "notes.read notes.write "
+        "calendar.read calendar.write "
+        "todo.read todo.write "
+        "contacts.read contacts.write "
+        "cookbook.read cookbook.write "
+        "deck.read deck.write "
+        "tables.read tables.write "
+        "files.read files.write "
+        "sharing.read sharing.write"
     )
     assert captured_env["NEXTCLOUD_OIDC_TOKEN_TYPE"] == "bearer"
     assert captured_env["NEXTCLOUD_MCP_SERVER_URL"] == "http://localhost:8000"