feat(workflows): Phase 5 ADO MG-PR verbs wired (replaces human-gate stub)

[PolyphonyRequiem]

feat(workflows): Phase 5 ADO MG-PR verbs wired (replaces human-gate stub)

Replaces the mg_pr_human_gate_ado stub in implement-mg.yaml with the
real pr open-mg-ado + pr merge-mg-ado verbs (shipped in PR #106 but
previously unwired because the workflow chain didn't thread the ADO
connection inputs).

What changed

polyphony-implement.yaml (1.1.0 → 1.2.0)

• New optional inputs: organization, project, repository (all
  default ""). Required only when platform=ado; ignored otherwise.
• Threaded down to implement-mg.yaml alongside the existing platform
  input.

implement-mg.yaml (1.0.0 → 1.1.0)

• New optional inputs: organization, project, repository.
• pr_platform_router now also computes ado_inputs_ready + missing
  so the workflow can fail early and clearly when platform=ado but the
  connection inputs are blank — without burning an ADO API call that
  would just return error_code: invalid_argument.
• Replaced mg_pr_human_gate_ado (operator-managed PR) with:
  • mg_pr_open_ado — script invoking polyphony pr open-mg-ado with
    --organization/--project/--repository. Idempotent (reuses an
    existing OPEN PR for the same head/base pair).
  • mg_pr_merge_ado — script invoking polyphony pr merge-mg-ado.
    Hardcoded merge-commit per the ADR (nested MGs depend on git
    ancestry; squash and rebase would break the chain). Idempotent
    (recognises an already-merged PR).
  • mg_pr_failed_gate_ado — human gate fired when either ADO verb
    returns a non-empty error_code (or merge returns merged=false).
    Retry routes back to mg_pr_open_ado (safe — both verbs are
    idempotent); abort routes to $end without invoking scope_closer.
  • mg_pr_inputs_missing_gate — human gate fired when platform=ado
    but one or more of organization/project/repository is blank.
    Surfaces the missing field list from the router so the operator can
    re-invoke with the correct inputs.
• output.pr_url and output.pr_number now prefer mg_pr_open_ado when
  defined, falling back to mg_pr_open (per M3 + M7).
• All routes use explicit error_code is defined and != '' /
  merged == true conditions plus a catch-all to the failure gate
  (per M4).

index.yaml

• Added missing implement-mg entry (was previously absent).
• Bumped polyphony-implement versions list to include 1.1.0 + 1.2.0
  (1.1.0 was already on disk but not tracked in the index — historical
  drift fixed in passing).

Scope decision (per rubber-duck pass)

This PR DOES NOT touch polyphony-full.yaml. Promoting platform to
the apex creates a misleading semantic where a full run with
platform=ado would still create GitHub plan PRs (because
plan-level.yaml is GitHub-only today). Operators wanting ADO MG
support should invoke polyphony-implement.yaml directly with
platform=ado + the three connection inputs, OR pre-author the plan
and start from ready_for_implementation. Apex-level platform threading
is deferred until plan-level + feature-pr ADO support land.

Validation

• All 16 lint scripts (8 ps1 + 8 Pester suites) pass.
• conductor validate passes for both touched workflows.
• 2400/2400 .NET tests pass.
• Verb signatures verified against the ADO MG verb help output and
  result schemas (PrOpenMgAdoResult, PrMergeMgAdoResult).

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com