Re-pin Interchange vendor trees to main head with the director loader

[TheGreatAxios]

Summary

• Re-pin all ten vendor/intx-* trees to Interchange main-head 1ad0104 (2026-09-13 sync), ahead of npm where the director-loader seam is unpublished.
• Vendor the workflow definition loader (workflow-definition-loader.ts + test) in vendor/intx-workflow-host/ for the director's sidecar-consumed tool-packaging seam.
• Record the written decision that @intx/tool-packaging stays a dependency, not a vendored tree (see docs/VENDORING.md).
• Re-carry the four patched trees with no entry dropped; kill backstops move to 2027-03-13.
• Adapt app code and tests to the new vendor credential surface (credentialId + readMaterial) with a documented identity resolver.

Verification

• bun run check passes: lint, typecheck, build, and the full suite (7465 pass, 1 skip, 0 fail — CI run 34809646114: test (src) 6397 pass + 1 skip, tests-evals-and-scripts 1068 pass).
• Branch rebased onto origin/main; vendoring only, no OAuth/credential runtime changes.

Fixes CL-7913

[linear-code]

CL-7913

[TheGreatAxios]

Closing as superseded by #1025, which landed the full re-vendor (pin to 1ad0104, director loader, ledger re-carry, first-party credential migration) with green reviews and gate. Merged as 7c41ba8.