[eric] docs: move the release runbook, checklist + squirrel plan into docs/ so root stops feeling cluttered

.github/workflows/phase-tests.yml

@@ -4,7 +4,7 @@ name: Phase tests (hermetic)
 # CI gate on each push/PR. These need no packaged artifact, no secrets, and no
 # network, so this job is fast and always meaningful. Phase tests that REQUIRE a
 # packaged build, signing, or real devices are NOT here (they can't be hermetic)
-# — those live in the smoke job below (manual) and RELEASE_CHECKLIST.md.
+# — those live in the smoke job below (manual) and docs/RELEASE_CHECKLIST.md.
 
 on:
   push:

scripts/run-phase-tests.js

@@ -3,7 +3,7 @@
 // packaged build, no network, and no platform assumptions, so they are safe in
 // CI and on any dev machine. Phase tests that REQUIRE a packaged artifact, CI,
 // macOS hardware, or a real device fleet are intentionally not here (they can't
-// be hermetic); see RELEASE_CHECKLIST.md for those.
+// be hermetic); see docs/RELEASE_CHECKLIST.md for those.
 //
 //   node scripts/run-phase-tests.js
 //