…-4 entry points

Adds the choice input current|namespace (default current) to the five
Phase 1-4 entry-point workflows. No runs-on or job behavior changes
yet — caller forwarding and runs-on ternary land in a follow-up commit.

Phase 0 of INFRA-3592.

…eusables

Adds the optional string input runner_provider (default current) to the
seven Phase 1-4 reusable workflows. Phase 7 reusables (runway-*, nightly,
testflight, etc.) are intentionally not modified — they continue to call
without forwarding, and the default keeps behavior byte-identical.

Phase 0 of INFRA-3592.

Adds with: runner_provider: ${{ inputs.runner_provider }} at every
in-scope caller site (55 sites across 7 caller workflows). Two iOS
build-ios-e2e.yml call sites had no with: block; a new minimal one
is added for them.

Phase 7 caller sites are intentionally not modified — push-eas-update,
nightly-build, runway-*, build-and-upload-to-testflight, build-rc-auto
continue to call without forwarding, the callee defaults to current,
and behavior is byte-identical.

Behavior is unchanged at this point: no runs-on consumes runner_provider
yet — that lands in I.3b.

Phase 0 of INFRA-3592.

Replaces every runs-on line in the in-scope Phase 1-4 workflows with the
additive ternary:

  runs-on: ${{ inputs.runner_provider == 'namespace' && 'nscloud-PLACEHOLDER-CONFIRM-LABEL' || <existing> }}

Where <existing> is the previous literal label or expression. Three sites
already had a ${{ ... }} platform ternary (build.yml setup-dependencies,
run-e2e-workflow.yml test-e2e-mobile, setup-node-modules.yml setup); for
those the existing expression is preserved verbatim inside the
runner_provider == 'namespace' || branch.

29 sites across 10 workflows. With runner_provider: current (the default
on every existing trigger), each ternary collapses to its prior literal
and behavior is byte-identical. The 'namespace' branch points at the
PLACEHOLDER label by design — replacement happens before any
runner_provider: namespace dispatch (see .phase0/namespace-artifacts.md).

Phase 0 of INFRA-3592.

…abels

Resolves Q1 of INFRA-3592 Phase 0. The four profile labels confirmed
live in the metamask Namespace workspace (format: namespace-profile-<name>):

  - namespace-profile-metamask-ci-linux       (Linux CI — Phase 1)
  - namespace-profile-metamask-android-build  (Android — Phase 3)
  - namespace-profile-metamask-ios-build      (iOS build / xl — Phase 4)
  - namespace-profile-metamask-ios-e2e        (iOS E2E test — Phase 4)

Each runs-on ternary now points at the profile that matches the existing
runner class (ubuntu-latest → ci-linux; macos-latest → ios-build; Cirrus
ubuntu-runner-amd64 → android-build; Cirrus macos-runner:tahoe-xl →
ios-build; Cirrus macos-runner:tahoe → ios-e2e). The three pre-existing
platform-driven dynamic expressions are preserved in both branches of
the ternary so Namespace dispatch follows the same iOS/Android branching
as the current runner choice.

actionlint.yaml drops the speculative nscloud-* and metamask-ci-linux
labels (never used) and registers the four canonical labels above.

Behavior on runner_provider: current is unchanged (every ternary still
collapses to its prior literal/expression).

Phase 0 of INFRA-3592.