Re-home the iOS host workflows

[TarikGul]

Same treatment as the Android workflows: re-created at the repository root and gated on the
host's change output, since workflows under a subdirectory are ignored.

Simulator builds need no signing identity. Device and store builds do, which is why this
depends on the configuration issue rather than assuming it.

Depends on: #678, #670, #672.

Steps

• Re-create the pull-request checks at the root, gated
• Re-create the signing and device-registration workflows, gated
• Re-create the distribution workflows, gated

Done when

A host-only pull request runs the host's checks, and a docs-only pull request runs none of
them.

[TarikGul]

Split into three, so the mechanical work could land without waiting on
credentials.

• ci(ios): re-home the dispatch-only iOS workflows to the repo root #728 moves the seven workflows that never trigger themselves. Nothing in it
  can run, so it changes no behaviour.
• ci(ios): re-home the remaining iOS workflows, held on dispatch #741 moves the remaining eight, the ones that run on pull_request or a
  schedule, with each live trigger commented out rather than deleted. The
  original filters and cron expressions are preserved exactly.
• A third, not yet open, restores those triggers. That is the change that puts
  iOS CI live, and it is now unblocked: every secret pr.yml reads is set.

All fifteen workflows are at the repository root after #741, none under
hosts/ios/.github/workflows/ where GitHub never read them.

Two things the third pull request has to decide rather than restore verbatim.
The branch filters name develop and main from the source repository's
branching model, and develop does not exist here. And nothing in either pull
request has been exercised by a run, so the first live trigger is also the first
real test of the path rewrites.

[TarikGul]

Blocked by #755. The re-homing itself is done and verified: #728 and #741 move all fifteen workflows, and on #754 the runners, signing, secrets and the in-tree core bootstrap all succeed. What fails is the app compiling against the core at HEAD, which is a real incompatibility rather than a CI problem.