Add legacy report rerun support for report outputs, simulations, and economy cache

[anth-volk]

Problem

The current legacy report flow in policyengine-api has no supported way to rerun a previously completed report.

That blocks the current app from offering a "rerun report" action, because the backend cannot reset the stored legacy state that makes the frontend think the work is already complete.

Today, rerunning a legacy report needs to do more than just clear the report row:

• report_outputs.output and report_outputs.error_message must be cleared
• the report status must go back to pending
• linked simulations.output and simulations.error_message may also need to be cleared
• linked simulation statuses may need to go back to pending
• economy report cache rows in reform_impact may need to be deleted so the economy calculation actually recomputes

Why This Is Annoying

There are a few legacy constraints that make this non-trivial:

• report_outputs rows are reused by simulation ids, year, and cache version
• simulations rows are reused by country, population, and policy
• the economy cache lives in reform_impact, which is keyed more broadly than the report row itself
• the existing update helpers only write output / error_message when the incoming value is non-None, so they cannot express a true reset-to-pending operation

Required Behavior

We need a supported legacy rerun path that:

1. loads the stored report_outputs row
2. loads the linked simulation row(s)
3. resets the report row to pending and clears persisted output/error state
4. resets the linked simulation row(s) to pending and clears persisted output/error state
5. for economy-shaped reports, deletes the matching reform_impact cache row(s)
6. returns a small success payload for the current app to consume

For the current legacy app path, economy reruns can use these assumptions when targeting reform_impact:

• dataset = "default"
• options_hash = "[]"
• time_period = report.year
• baseline_policy_id = simulation_1.policy_id
• reform_policy_id = simulation_2.policy_id when present, otherwise simulation_1.policy_id
• region = simulation_1.population_id
• api_version = current economy cache version

That assumption set is correct for the current app-generated legacy flow, but should not be mistaken for a universal provenance model for all historical legacy callers.

Acceptance Criteria

• legacy services expose explicit reset helpers for reports and simulations
• economy cache deletion can remove completed cache rows, not just computing rows
• POST /<country_id>/report/<report_id>/rerun exists
• household reruns clear report and simulation persisted output
• economy reruns also delete matching reform_impact rows
• malformed linked-simulation state returns a controlled error without partially mutating stored rows
• tests cover household, economy, and malformed-linkage cases