feat(sdk): offline W&B export migration — ExportDirSource + from_wandb_export.py (GLA-844)

[jqueguiner]

Summary

• sdk/openrunner/migrate.py — refactored into WandbRunSource protocol with LiveAPISource (preserves existing behaviour) and ExportDirSource (new offline path). Adds migrate_from_wandb_export() public entry-point.
• sdk/openrunner/cli.py — adds --from-wandb-export <path> flag to openrunner migrate.
• examples/migrate-from-wandb/from_wandb_export.py — standalone CLI wrapper; thin argparse shim over migrate_from_wandb_export. Fixes the missing source file (only __pycache__/from_wandb_export.cpython-312.pyc existed on main).
• examples/migrate-from-wandb/README.md — usage guide, prerequisites, export layout, and import asset table.
• sdk/tests/test_migrate.py — unit tests for ExportDirSource + migrate_from_wandb_export with the wandb-export-mini fixture set.
• sdk/tests/fixtures/wandb-export-mini/ — test fixtures (two run dirs with config, metrics, artifacts, summary).

Supersedes #111 (which added only the example file without the required migrate_from_wandb_export SDK entry-point, making the script non-functional at runtime).

Closes GLA-844.

Test plan

• python examples/migrate-from-wandb/from_wandb_export.py --help shows usage
• python examples/migrate-from-wandb/from_wandb_export.py /nonexistent --dry-run exits with code 2 and error on stderr
• pytest sdk/tests/test_migrate.py passes
• CI green

🤖 Generated with Claude Code

[jqueguiner]

MergeEngineer cycle check — GLA-849

CI status:

• ✅ SDK Tests, Frontend Type Check, Docker Build, Docs — green
• ✅ Artifact Round-Trip Smoke, docker compose + SDK round-trip — green
• ⏳ Backend Tests — in progress (run tests with coverage step running)

Hold: reviewDecision = REVIEW_REQUIRED — no approvals yet. Per auto-merge contract, this PR needs APPROVED before it can merge.

Branch principal/gla-844-wandb-export indicates PE authored this work. Request: please approve on GitHub so I can merge once Backend Tests pass.

[jqueguiner]

Closing — and already landed on main via commit 9b152b7 (feat(sdk): W&B offline export migration — GLA-834/GLA-610). All GLA-826 acceptance criteria met. PR #112 is superseded.

[jqueguiner]

MergeEngineer: rebased onto main at 9b152b7 — resolved trivial conflict in sdk/openrunner/migrate.py (tarfile compat shim, took main's version). CI re-running. Will merge once CI green + @jqueguiner approves (PR requires REVIEW_REQUIRED → APPROVED; author cannot self-approve).