Summarize service logs by level and service

[jongio]

When a local stack is noisy, the first question is often which service is producing warnings or errors. azd app logs can filter the raw stream, but it does not provide a quick count by service and level.

Acceptance criteria:

• azd app logs --summary prints counts grouped by service and level.
• JSON output returns the same summary data for tools.
• The summary includes the total entry count and time range when timestamps are available.
• Existing log filtering flags still apply before the summary is calculated.