Description

Closes APP-1055.

Makes the "Download actions" export reusable and wires it into the two places that were still missing it: the standalone
ProposalActionsEditor and the read-only cross-chain forwardMessage details view.

• useDownloadProposalActions — extracted verbatim from CreateProposalFormActions into
  modules/governance/hooks. Reads actions from the surrounding form, runs the registered prepare functions
  (proposalActionPreparationUtils.prepareActions, so actions needing async work such as IPFS pinning export their
  final calldata) and downloads the result. Returns { isPinning, hasPinErrors, handleDownloadActions }. daoId is
  optional and only decides the file name (dao-{daoId}-actions.json, else actions.json), so the hook also works
  outside a DAO context.
• CreateProposalFormActions now consumes that hook instead of holding the pinning state and download callback itself —
  no behaviour change.
• ProposalActionsEditor gains the same download support, passing isPinning / hasPinErrors / onDownloadActions
  through to ActionComposer. Previously the button was only available in the create-proposal form.
• CrossChainControllerForwardMessageDetails gets a "Download actions" button below the nested actions list, exporting
  the raw Action[] tuples decoded from the _message payload as cross-chain-{chainId}-actions.json. The button is
  hidden when the message holds no actions. This path does not go through useDownloadProposalActions: the sub-actions
  are already-encoded calldata read back from a published proposal, so there is nothing to prepare and no form context
  to read from.
• proposalActionsImportExportUtils — exportActionsToJSON / downloadActionsAsJSON now accept
  IExportableAction (Pick<IProposalAction, 'to' | 'value' | 'data'>) instead of the full IProposalAction, which is
  what lets the raw cross-chain tuples be exported without being faked into proposal actions.
• Tests: new suite for useDownloadProposalActions (prepare-then-download, file naming, error path), download coverage
  for the cross-chain details view, and createProposalFormActions.test.tsx now spies on useDownloadProposalActions
  (the component's actual dependency) rather than the form-provider context.

Dependencies: stacked on app-1032-implement-action-decodingdetails-view → app-1054-… → app-1056-… → app-1053-…
→ main. Merge the bases first. Last PR of the stack (10/10).

Type of Change

• Minor: Feature (non-breaking change which adds new functionality)

Developer Checklist:

• Manually smoke tested the functionality in a preview or locally
• Confirmed there are no new warnings or errors in the browser console
• (For User Stories only) Double-checked that all Acceptance Criteria are satisfied
• Confirmed there are no new warnings on automated tests
• Merged and published any dependent changes in downstream modules
• Selected the correct base branch
• Commented the code in hard-to-understand areas
• Followed the code style guidelines of this project
• Reviewed that the Files Changed in Github's UI reflect my intended changes
• Confirmed the pipeline checks are not failing

Review Checklist:

• (For User Stories only) Tested in a preview or locally that all Acceptance Criteria are satisfied
• Confirmed that changes follow the code style guidelines of this project