Enable shared report actions with strict read-only config view

[anth-volk]

Problem

Shared reports currently behave like a special case in ways that block normal viewing workflows.

Today:

• shared report output does not expose the same header actions that owned reports expose
• users cannot move from a shared report into the report configuration view without saving first
• the share UI is inconsistent with the rest of the app
• breadcrumb/back-link behavior around report output, config, and reproduce is inconsistent
• shared setup needs a hard read-only guarantee so users can inspect configuration without ever being able to edit it

Desired behavior

We should support the normal report-viewing actions in shared mode wherever they are safe:

• show the same report output action buttons in shared mode that we show in owned mode
• allow users to open the report configuration screen from shared reports
• allow users to open reproduce-in-python from shared reports
• keep shared setup strictly read-only at the page and modal level
• make the share interaction look like native app UI instead of a generic alert
• make breadcrumbs consistently return users to the report they were viewing

Constraints

This needs to avoid reopening the recent routing and calculation-state regressions. In particular:

• do not expand the scope into report calculation orchestration or query-hook refactors
• keep the report setup/config route client-side and lightweight
• shared mode must not allow any write path to slip through via nested modals or policy editors