feat(handoff): enable reports by default

[Zxf-xufeng]

Which issue or RFC does this PR close?

Closes #1254

Rationale for this change

Handoff Report is already implemented, but its default opt-in setting makes the Dashboard page difficult to discover. The Dashboard should expose the existing Handoff Report interface by default while keeping the statistics Dashboard at / and preserving an explicit opt-out.

What changes are included in this PR?

• Change HandoffReportConfig.enabled default from false to true.
• Keep handoff_report.enabled=false as the explicit opt-out path.
• Update the HTTP test to verify that the opt-out still prevents Report-owned tables from being created.

Are there any user-facing changes?

With default settings, an authenticated Dashboard deployment exposes the Handoff Report page and navigation entry. The existing statistics Dashboard remains at /; this change does not redirect / to /handoff-reports or automatically select the Handoff Report tab. Core Handoff behavior is unchanged.

How was this change tested?

• env -u POWERCONTEXT_SERVER_AUTH_ENABLED -u POWERCONTEXT_SERVER_AUTH_TOKEN -u POWERCONTEXT_SERVER_DASHBOARD_ENABLED -u POWERCONTEXT_SERVER_DASHBOARD_SCOPES uv run pytest -q tests/test_dashboard.py tests/test_handoff_report_http.py
• Result: 6 passed.

AI usage statement

Implemented and validated with OpenAI Codex (GPT-5).

[CLAassistant]

All committers have signed the CLA.

[Teingi]

LGTM