feat: show email preview snippet in thread list tiles

Added preview field to EmailThread (from latest email's preview via
_groupIntoThreads). Thread tiles now show subject + one-line body snippet.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

done.md

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+# Done
+
+This file contains tasks which got implemented.
+
+Tasks get moved from next.md to done.md
+
+## Tasks
+
+## Show email preview snippet in list
+
+Added `preview` field to `EmailThread` (populated from the latest email in
+`_groupIntoThreads`). Thread tiles now show subject + a one-line preview
+snippet in the subtitle.
+
+## Extract TryConnectionButton widget shared by account screens
+
+Extracted `lib/ui/widgets/try_connection_button.dart` — a stateless widget
+rendering the result banner (ok/error text) and the spinner/button. Both
+`add_account_screen` and `edit_account_screen` now use it, removing ~30 lines
+of duplicated UI code.
+
+## Extract _batchMoveToRole helper in email_list_screen
+
+`_batchArchive()` and `_batchMarkSpam()` collapsed into a shared
+`_batchMoveToRole(role, notFoundMessage)` helper, eliminating ~20 lines of
+duplication.
+
+## Enable always_use_package_imports lint rule
+
+Added rule to `analysis_options.yaml`; `dart fix --apply` converted 125 relative
+imports across 33 files to `package:sharedinbox/...` style automatically.
+
+## Replace silent catch (_) with logged errors
+
+5 `catch (_)` blocks in JMAP push stream setup and 2 in UI screens now use
+`catch (e)` with `log(...)` via the project's `logger.dart` wrapper.
+The two intentionally silent catches (malformed SSE JSON, Sent folder already
+exists) were left as-is since they already had explanatory comments.
+
+## Safety hardening before real account use
+
+### 1. Fix non-PEEK body fetch (silently sets \Seen)
+
+`lib/data/repositories/email_repository_impl.dart` ~line 163
+Change `'(BODY[])'` → `'(BODY.PEEK[])'` so fetching the body does not set \Seen
+as a side-effect of the IMAP FETCH command.
+
+Same fix at ~line 1696 for attachment part fetches: `BODY[partId]` → `BODY.PEEK[partId]`.
+
+### 2. Move to Trash instead of EXPUNGE
+
+`lib/data/repositories/email_repository_impl.dart` `deleteEmail` method
+Before enqueuing a hard delete, query the local mailboxes cache for a 'trash'-role
+folder for that account.
+
+- If found AND the email is not already in Trash: call `moveEmail` to that path.
+- If not found OR already in Trash: fall back to the existing EXPUNGE path.
+
+This makes delete reversible — the user can recover from Trash.
+
+### 3. Confirmation dialog for delete
+
+Three call sites need a `showDialog` confirmation before deleting:
+
+a) Delete button in detail view
+   `lib/ui/screens/email_detail_screen.dart` ~line 97
+   Show AlertDialog "Delete this email?" with Cancel / Delete buttons.
+
+b) Batch delete in list view
+   `lib/ui/screens/email_list_screen.dart` `_batchDelete` ~line 268
+   Show AlertDialog "Delete N emails?" with Cancel / Delete buttons.
+
+c) Swipe-to-delete in list view
+   `lib/ui/screens/email_list_screen.dart` `Dismissible.onDismissed` ~line 436
+   Use `Dismissible.confirmDismiss` callback (fires before the item is removed)
+   to show a confirmation for the right-swipe (delete) direction only.
+   Return false to cancel and keep the item in the list.