feat: add transferred-repo flag in deploy.yml to skip Vercel deploys cleanly

[taprile314]

Problem & Motivation

When a custom-code repo is transferred to a client's Vercel team, deploys keep firing and fail with a generic error. This (a) generates constant noise and (b) blocks any useful org-wide alert on consecutive Vercel-deploy failures. Recent postmortem: the noise conflated two distinct issues during initial diagnosis and low weekend merge activity hid the real failure for ~48h.

Scope & Decomposition

• Add a transferred input (default false) to the deploy.yml reusable in platform. When true, the deploy job logs a skip message and exits 0 without invoking Vercel.
• Update the callers of the two transferred repos (umh-custom-code, profile-behavior-custom-code) to pass transferred: true.
• Document the pattern in platform/README.md (when to use, how to set the flag, how to verify).

Note: org-wide alert on consecutive Vercel-deploy failures will be tracked in a separate issue, blocked by this one (the alert is only useful once the flag eliminates transferred-repo noise).

Acceptance Criteria

• deploy.yml reusable accepts a transferred input (default false); when true, the deploy job logs a skip message and exits 0 without invoking Vercel.
• umh-custom-code and profile-behavior-custom-code callers pass transferred: true and stop producing failed runs.
• Pattern documented in platform/README.md (when to use, how to set the flag, how to verify).

Risks & Constraints

• If the flag is set by accident on an active repo, deploys silently succeed (skipped) without error — the skip log message must be visible and grep-able.
• The reusable changes its contract (new input) — all callers pinned to @v1 will see it, so the input MUST have default false to avoid breaking anyone.

Edge Cases

• Transferred repo whose caller still runs ci jobs — the flag must affect only the deploy, not CI (lint/typecheck/test/build remain useful if someone is still maintaining the repo).
• "Semi-transferred" repo where we still want CI but not deploy — covered by the previous point.

Sub-issues

Work each sub-issue on its own branch, opening PRs against the epic branch. Merge the epic branch into main when all sub-issues are complete.

• Add transferred input to deploy.yml reusable #21 � Add transferred input to deploy.yml reusable
• Update transferred callers (umh-custom-code, profile-behavior-custom-code) to pass transferred: true #22 � Update transferred callers (umh-custom-code, profile-behavior-custom-code) to pass transferred: true
• Document the transferred-repo pattern in platform/README.md #23 � Document the transferred-repo pattern in platform/README.md