docs: close diagnostics migration debt

[Pluze]

Goal and scope

• Goal: remove the completed diagnostics migration from the active debt ledger.
• In scope: mark architecture and compatibility debt as none and delete the resolved execution roadmap.
• Intentionally out of scope: product, framework, App, test, generated-site, version, and history changes.

User-visible behavior

• Before: the migration ledger still described work already merged into both repositories.
• After: the ledger contains only current debt state and its stable maintenance rules.
• Compatibility / upgrade note: none; this is agent-governance cleanup only.

Validation

• I ran the smallest relevant local validation from docs/development/maintain-and-release/testing.md.
• I ran the required final gate for this handoff, or this PR is not ready for final review.
• Automated validation was not run; reason and risk are recorded below.

Commands and results:

git diff --check
PASS

Public migration PR main@371aa3f8
PASS: Continuous Integration, including aggregate CI Gate

Private migration main@2965196 against public main@371aa3f8
PASS: local private MATLAB suite, 48/48

Manual / native behavior not verified:

• No manual product behavior is changed by this ledger-only cleanup.

Documentation and boundaries

• Human docs were updated where user-facing behavior or public contracts changed.
• Agent guidance was updated where execution, ownership, or governance rules changed.
• Docs and agent guidance were left unchanged because their contracts were preserved.
• Versioned component docs and a related docs/history/records/**/*.md record were updated where required.
• App-specific workflow logic stayed in the owning app.
• Reusable +labkit changes, if any, are domain-neutral and app-facing.

Delivery state

• The branch is committed and pushed.
• Required GitHub checks are linked below, or are pending:

CI / review links:

• Pending on this ledger-only PR.

Data hygiene

• This PR does not add raw lab files, identifying file names, subject names, device serials, local absolute paths, timestamps, or private experiment labels.

Unverified behavior

• None for this documentation-only change.