refactor: rename returnOnly to subObservationMode for clarity in form handling

[Mishael-2584]

Description

Follow-up to the sub-observation / embedded child-form work: rename the init and openFormplayer flag from returnOnly to subObservationMode, tidy formplayer draft handling, and drop noisy logging on the no–persist path.

What changed

Area	Change
Bridge contract	FormInitData and openFormplayer options use subObservationMode?: boolean (see formulus/src/webview/FormulusInterfaceDefinition.ts).
Native (Formulus)	App.tsx, FormplayerModal.tsx, and FormulusMessageHandlers.ts pass/read the new field; formInitData uses subObservationMode.
Compatibility	Older bundles that still send returnOnly (top-level or under options) are still honored for one transition period.
Formplayer	Types synced from Formulus; App.tsx uses subObservationMode and merges the draft-session reset when subObservationMode || observationId != null (with the same legacy read where applicable).
Logging	Removed the success-path console.log in FormplayerModal for the path that does not save to the DB.

Files touched (high level)

Package	Paths
formulus	App.tsx, src/components/FormplayerModal.tsx, src/webview/FormulusInterfaceDefinition.ts, src/webview/FormulusMessageHandlers.ts
formulus-formplayer	src/App.tsx, src/types/FormulusInterfaceDefinition.ts (via npm run sync-interface)

How to verify

• Open a flow that uses embedded child / sub-observation mode and confirm the child session still returns JSON to the parent and does not create a stray top-level observation.
• Smoke-test a bundle that still sends returnOnly (if you have one) to confirm it still works.

Notes

• Run npm run sync-interface (and your usual npm run build:rn in formulus-formplayer if you ship RN-bundled assets) before merging or releasing.
• If npm run generate for the WebView injection script fails in your environment, it is separate from this rename; native handling of options is what matters for the new key.

[najuna-brian]

Confirmed working
Thanks @Mishael-2584