fix(kagent-adk): compact MCP App tool results only when the result carries a UI resource

[AmirF194]

Root cause

compact_mcp_app_response (python/packages/kagent-adk/src/kagent/adk/_mcp_apps.py)
collapses a tool's result into a terminal notice whenever the tool's name is in
app_tool_names, a set populated once from the tool's _meta.ui.resourceUri at
ListTools time. A single tool can carry a UI mode without every call rendering it
(the issue's example: an Atlassian search tool with a UI widget), so any plain,
data-only result from such a tool was silently replaced with the notice text for a
headless caller (A2A, kagent invoke), with no error.

Fix

Added _result_has_ui_resource, which checks the result's own _meta.ui.resourceUri
/ _meta["ui/resourceUri"], the same fields go/adk/pkg/mcp/mcp_ui.go already parses
to classify a tool's definition, applied here to the per-call result instead.
compact_mcp_app_response now passes a result through unchanged unless it declares a
UI resource itself.

Scoped to the Python ADK runtime per the issue; go/adk/pkg/agent/mcp_apps.go has the
identical gap and is left as a follow-up, since it is outside this change's surface.

Verification

• New tests reproduce the issue directly: a data-only result from a UI-capable tool
  (empty _meta, and no _meta key at all) now passes through unmodified. Both fail
  on main (asserting the old collapse) and pass on this branch; confirmed independently
  in a clean container against an unmodified worktree of main before rebuilding on the
  branch.
• Full kagent-adk unit suite (uv run pytest packages/kagent-adk/tests/unittests/):
  402 passed on Python 3.11 and 3.13, both CI matrix extremes.
• ruff check and ruff format --diff on the two changed files: clean.
• Not verified: a real MCP server whose result carries a UI resource via a content
  block rather than _meta (no such server available to test against); the existing
  and new tests all key on _meta, matching the only shape this repo's own tests and
  mcp_ui.go currently recognize.

Fixes #2519