ci: replace 14 workflows with 4-tier orchestrator

Replaces 14 CI workflows with a single ci-orchestrator.yml that runs
jobs in a 4-tier waterfall. Tiers gate each other sequentially: if
formatting fails in 2 minutes, nothing else runs.

Every job carried over from the old workflows was optimized along the
way. Jobs use native container: blocks instead of the old
addnab/docker-run-action wrapper, cache scopes were split and tuned
(hit rates went from ~48% to 99%+), SITL tests run at 20x speed on
8cpu runners, clang-tidy got a dedicated 16cpu runner and cache, the
failsafe sim caches its emsdk, and flash analysis posts sticky PR
comments.

Forks can use this without AWS infrastructure. Copy
.github/ci-config.yml.example to .github/ci-config.yml to customize
runner labels, job toggles, and cache sizes. Alternatively, rename
.github/workflows/ci-simple.yml.example to ci-simple.yml for a
single-job workflow that finishes in under 15 minutes on ubuntu-latest.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/ci-simple.yml.example

@@ -0,0 +1,41 @@
+name: Simple CI (Fork-Friendly)
+
+# Forks: This is a lightweight CI workflow for forks that don't need
+# the full orchestrator pipeline. It builds PX4 SITL + one hardware
+# target and runs unit tests + format checks.
+#
+# To use: rename this file from ci-simple.yml.example to ci-simple.yml
+# and enable GitHub Actions in your fork settings.
+# To customize: adjust the 'make' target or container image tag below.
+
+on:
+  push:
+    branches: ['**']
+  pull_request:
+    branches: ['**']
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  quick-check:
+    runs-on: ubuntu-latest
+    container:
+      image: ghcr.io/px4/px4-dev:v1.17.0-beta1
+    steps:
+      - name: Configure git
+        run: git config --system --add safe.directory '*'
+
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          submodules: recursive
+
+      - name: Quick Check (SITL + FMUv5 + tests + format)
+        run: make quick_check
+        env:
+          RUNS_IN_DOCKER: true