fix: /new modal path picker not applying on web + persist “new session” draft state locally

[leeroybrun]

Context / Problem

• On web builds, the /new modal uses nested routes (/new/pick/path, /new/pick/machine) to select machine/path.
• Selecting a new path (or machine) and pressing Apply would sometimes not update the /new modal — it would snap back to the original value.

Root cause

• The picker screens were communicating back to /new via module-level mutable callbacks exported from the /new route module.
• On web, modal navigation and route transitions can cause screens/modules to be unmounted/remounted or re-instantiated in ways that break this “global callback bridge”, so the picker’s “Apply” effectively became a no-op for the active /new instance.

Fix 1: Replace callback bridge with navigation params

• Removed the module-global callback mechanism.
• Pickers now pass the selection back using React Navigation params (CommonActions.setParams) targeting the previous route.
• /new listens to the returned params via useLocalSearchParams() and updates selectedMachineId / selectedPath accordingly.
• This approach survives remounts and is consistent with navigation semantics (no hidden cross-module state).

Fix 2: Persist the /new draft locally (lightweight, no UI changes)

• Added a minimal MMKV-backed “new session draft” stored under new-session-draft-v1.
• The draft includes: input text, selected machine/path, agent type, permission mode, session type, and updatedAt.
• /new initializes from this draft when opened, auto-saves changes with a small debounce, and clears the draft after successful session creation.
• This makes the flow resilient to navigation/remounts and also preserves user input if the modal is closed/reopened.

Files touched

• sources/app/(app)/new/index.tsx: remove callback bridge, apply param-driven updates, load/save/clear new-session draft.
• sources/app/(app)/new/pick/machine.tsx: set previous route params instead of calling callbacks.
• sources/app/(app)/new/pick/path.tsx: set previous route params instead of calling callbacks.
• sources/sync/persistence.ts: add MMKV helpers + types for new-session draft.

How to test

• Web:
  • Open http://localhost:3005/new
  • Type a prompt, change path via picker, hit Apply → /new updates to the selected path.
  • Navigate away and back / close and reopen /new → prompt + selections are restored.
  • Create session → draft is cleared.