ci: gate every compile job from one change filter

[TarikGul]

Warning

Do not merge while R2 is in flight. This is parked deliberately, not
waiting on review. Nothing depends on it yet: the host imports it prepares
for do not start until after the release, so merging it now buys nothing
this month and puts a CI change into a release window.

Two things must happen before it merges:

• R2 has shipped.
• Confirm ci-android / build and iOS change filter are not
  required status checks. This branch removes the first and renames the
  second, and a required check that no longer reports blocks every merge.
  CI Status is the check to require.

Summary

ci.yml computes every path gate in one place. A changes job publishes
sdk_swift and sdk_kotlin, and each gated job reads the output it cares
about. ci-status aggregates every job in the workflow and counts a job
skipped by its filter as a pass, which makes it the single check worth
requiring.

This is the gating spine the host imports build on: adding a host means adding
one output and one consumer, not another workflow with its own trigger.

Why the Android compile gate lives here

In its own workflow with a paths trigger it reported nothing at all on a pull
request touching other areas, so it could never satisfy a required status
check. It also had no merge_group trigger, so the Kotlin shell went
uncompiled on merge queue runs. As a gated job it reports skipped when it does
not apply, and it runs on the merge queue with everything else.

Its steps are carried over unchanged, including the codegen step that the
gitignored generated modules require.

Filter behaviour

Change	sdk_swift	sdk_kotlin
docs/ only	false	false
playground/ only	false	false
ios/	true	false
android/	false	true
js/container/	true	false
rust/crates/truapi-provider/	true	false
rust/crates/uniffi-bindgen-cli/	false	true
rust/crates/truapi/	true	true
rust/crates/truapi-server/	true	true
Makefile	true	true
.github/workflows/ci.yml	true	true

The Kotlin filter names rust/crates/truapi for the same reason the Swift
filter does: neither binding set is committed, so a protocol change there
leaves no android/ diff to key on.

Both filters name this workflow, so this pull request exercises both gates.

Known cost

The Kotlin gate now also evaluates on rust/crates/truapi and Makefile
changes, and on merge queue runs. That job runs npm ci, codegen, a Rust build
and a Gradle build, so it adds merge queue latency. The old filter already
covered rust/crates/truapi-server/**, which most protocol changes touch, so
the widening is smaller than the table suggests.

rel: #636