Add internal services for report output runs

[anth-volk]

Fixes #3427

Summary

This PR implements stage 2 of the report-output run migration plan.

It adds internal services and tests for:

• typed report specs
• typed simulation specs
• explicit legacy report alias resolution
• report run creation and selection
• simulation run creation and selection

What changes for consumers

Nothing yet.

This is an internal service-layer PR only. Routes, response shapes, and runtime behavior stay the same.

What does not change

• no endpoint contract changes
• no route integration yet
• no backfill
• no dual-write
• no rerun behavior change

Safety

• isolated internal service layer
• no production behavior changes
• focused unit coverage for every new service

Verification

FLASK_DEBUG=1 uv run pytest --confcutdir=tests/unit \
  tests/unit/services/test_report_spec_service.py \
  tests/unit/services/test_simulation_spec_service.py \
  tests/unit/services/test_report_output_alias_service.py \
  tests/unit/services/test_report_run_service.py \
  tests/unit/services/test_simulation_run_service.py

[codecov]

Codecov Report

❌ Patch coverage is 77.41117% with 89 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.56%. Comparing base (3bd5d4f) to head (5e15e2f).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
policyengine_api/services/report_spec_service.py	68.83%	28 Missing and 20 partials ⚠️
policyengine_api/data/data.py	48.33%	27 Missing and 4 partials ⚠️
...licyengine_api/services/simulation_spec_service.py	88.37%	2 Missing and 3 partials ⚠️
...olicyengine_api/services/simulation_run_service.py	94.00%	2 Missing and 1 partial ⚠️
policyengine_api/services/report_run_service.py	96.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3428      +/-   ##
==========================================
+ Coverage   73.03%   73.56%   +0.53%     
==========================================
  Files          56       61       +5     
  Lines        2629     3015     +386     
  Branches      463      538      +75     
==========================================
+ Hits         1920     2218     +298     
- Misses        622      680      +58     
- Partials       87      117      +30     

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