fix(journal): flush autosave on dismiss, import reload, and midnight rollover

[cursor]

Summary

Re-applies validated journal autosave fixes still missing from main (same class as open PR #619). Three concrete data-loss paths:

1. Background / dismiss before debounce — Today edits only persisted after 400ms debounce; backgrounding or leaving the screen could drop in-flight chip/notes edits.
2. Import + warm Today VM — Settings import ran on a detached ModelContext while Today held stale in-memory state; a pending debounced autosave could overwrite freshly imported today row.
3. Midnight rollover with inline chip draft — Uncommitted inline chip text could be lost when the calendar day advanced; stale editing indices could write into the new day.

Root cause

• No immediate flush on scenePhase background/inactive or onDisappear.
• No epoch guard on debounced autosave after external store changes.
• Import did not notify Today to reload; used background context.
• Day rollover did not commit/dismiss inline chip editing before reload.

Fix

• persistImmediately() + commitActiveInlineChipEdit() on background/inactive and disappear.
• autosaveEpoch invalidates stale debounced saves; reloadFromStoreAfterExternalChange after import.
• Import on main modelContext + journalStoreDidChangeExternally notification.
• Commit/dismiss inline chips before midnight rollover; reset chip UI after reload.
• Skip day rollover when persist fails (avoid loading today without saving yesterday).

Validation

• swiftlint lint (Linux)
• Added/updated unit tests: JournalViewModelTests, JournalViewModelExternalReloadTests
• Full simulator test run requires macOS (grace test)