docs(fdroid): warn against premature submodules:true in official recipe

fdroidserver's initsubmodules() raises NoSubmodulesException on any build
entry whose commit lacks .gitmodules, so `submodules: true` is a hard build
failure on every release before the floret-kit submodule lands (verified
2026-06-28 against fdroiddata MR !41553). Document that it must be added
only in the recipe entry targeting the first release that ships the
floret-kit composite build.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/fdroid-official/de.jeanlucmakiola.calendula.yml

@@ -48,6 +48,19 @@ Builds:
     # No NDK / no flavors. The release buildType applies a signingConfig only
     # when key.properties exists; on the buildserver it does not, so this
     # produces the unsigned APK F-Droid compares against our binary.
+    #
+    # DO NOT add `submodules: true` here ahead of need. fdroidserver's
+    # initsubmodules() RAISES NoSubmodulesException ("No git submodules
+    # available") on any build entry whose commit has no `.gitmodules`, so
+    # `submodules: true` is a HARD BUILD FAILURE — not a no-op — on every
+    # release before the floret-kit submodule lands. (Verified 2026-06-28: it
+    # broke the fdroid build / checkupdates / check-source-code jobs on
+    # fdroiddata MR !41553; confirmed locally with the fdroidserver-master
+    # fetchsrclibs path.) Add `submodules: true` ONLY in the recipe entry that
+    # targets the FIRST release actually shipping the `floret-kit` git submodule
+    # (composite build via `includeBuild("floret-kit")`, core-time refactor on
+    # branch `chore/floret-kit-core-time`) — and only there. From that entry on
+    # it becomes the AutoUpdateMode template and propagates to future builds.
 
 # SHA-256 of our app signing certificate (public; embedded in every published
 # APK). Locks F-Droid to publish only binaries signed with our key.