v2 portability: restore legacy provisioner

[josephjclark]

@midigofrank's eagle eyes showed me something I had missed: the portability updates should not have removed support for v1 formats from the provisioner API.

This PR restores the v1 emmiter and provisioner, but leaves the UI stuff on v2.

Description

• Restored the v1 emitter in lib/lightning/export_utils.ex (verbatim from main).
• Routed by surface, not by a global default. Projects.export_project/4 now takes a required positional format argument (:v1 | :v2, no default) and dispatches accordingly:
  -DownloadsController ("Export project as YAML" download) → :v2
  • ProvisioningController.show_yaml (GET /api/provision/yaml, used by openfn pull and GitHub sync) → :v1, hard-coded - no version parameter is exposed on the API.
• The frontend "View workflow as code" panel stays on v2 (separate JS code path, untouched).
• The provisioner's POST /api/provision is unaffected — it has always accepted JSON, not YAML.
• Forced v2 yamls to use lower-case id names

QA Notes:

• ✅ Can pull with legacy cli openfn pull <uuid>
• ✅ Can edit and push with legacy cli openfn deploy <uuid>
• ✅ Exported workflows can be executed through CLI
• ✅ Exported projects can be checked out with CLI (just pass the file name)
• ✅ v1 app workflows can be imported into this branch
• ✅ v2 app workflows can be imported into this branch

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[github-actions]

Security Review

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[codecov]

Codecov Report

❌ Patch coverage is 96.68874% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.87%. Comparing base (164c0bf) to head (d95df3e).

Files with missing lines	Patch %	Lines
lib/lightning/export_utils.ex	96.55%	5 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##           v2-sync-finalization    #4743      +/-   ##
========================================================
- Coverage                 89.88%   89.87%   -0.01%     
========================================================
  Files                       444      445       +1     
  Lines                     22112    22259     +147     
========================================================
+ Hits                      19876    20006     +130     
- Misses                     2236     2253      +17     

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