…LK#2)

* feat(client): local-first cache, virtualized list, optimistic UI

Implements the client-side optimization tier from the Email 2.0 proposal
(Phase 2 + parts of Phase 5): instant warm loads, smooth scrolling over
large mailboxes, and instant actions. No backend/protocol changes.

- IndexedDB cache (Dexie), scoped per account email, for mailbox-list
  rows and message bodies. All reads/writes are failure-tolerant so a
  cache error can never break the app.
- Cache-first rendering: inbox/sent/trash paint from IndexedDB before the
  network responds, then refresh in the background with no blocking
  spinner. A failed folder fetch no longer clobbers good cached rows.
- Cache-first message bodies: reopening a thread paints instantly, then
  revalidates; a revalidation error won't blank an already-painted body.
- Optimistic markAsRead/deleteThread with rollback on failure.
- Virtualized ThreadList via @tanstack/react-virtual.

Adds deps: dexie, @tanstack/react-virtual.

* feat(client): infinite-scroll pagination beyond the first 50 messages

The inbox previously loaded only the newest 50 messages per folder with no
way to see older mail. Adds cursor-based pagination on top of the
virtualized list:

- DataContext tracks a per-folder `before` UID cursor, `hasMore`, and
  `loadingMore`, and exposes loadMore(role). loadAll records the first
  page's cursor; loadMore fetches the next page (de-duped) and appends to
  state + IndexedDB cache.
- ThreadList auto-loads the next page when the last row scrolls into view
  (react-virtual), with a footer spinner while fetching.
- Inbox/Sent/Trash wire loadMore for their role. Pagination is suppressed
  while a search query is active (client-side search only filters loaded
  rows). The backend already supported the `before` cursor + next_before.

* feat: Gmail-style paged navigation ("1–50 of N") instead of infinite scroll

Replaces the append-on-scroll pager with classic page controls: a
"start–end of total" label and prev/next arrows above the list.

Backend:
- imap.ListMessages also returns the mailbox total (mbox.Messages);
  the messages endpoint includes it as `total` for the "of N" count.

Frontend:
- DataContext tracks page/total/pageLoading per folder plus a per-page
  `before` cursor history (ref), and exposes nextPage/prevPage that
  REPLACE the visible page (forward cursor discovered from next_before,
  back reuses the stored cursor). Only page 0 is mirrored to the cache.
- ThreadList renders the pager bar above the virtualized scroll area and
  resets scroll to top on page change.
- Inbox/Sent/Trash wire prev/next for their role; the pager is hidden
  while a search query is active (search filters the loaded page only).

…LK#2)

* feat(client): local-first cache, virtualized list, optimistic UI

Implements the client-side optimization tier from the Email 2.0 proposal
(Phase 2 + parts of Phase 5): instant warm loads, smooth scrolling over
large mailboxes, and instant actions. No backend/protocol changes.

- IndexedDB cache (Dexie), scoped per account email, for mailbox-list
  rows and message bodies. All reads/writes are failure-tolerant so a
  cache error can never break the app.
- Cache-first rendering: inbox/sent/trash paint from IndexedDB before the
  network responds, then refresh in the background with no blocking
  spinner. A failed folder fetch no longer clobbers good cached rows.
- Cache-first message bodies: reopening a thread paints instantly, then
  revalidates; a revalidation error won't blank an already-painted body.
- Optimistic markAsRead/deleteThread with rollback on failure.
- Virtualized ThreadList via @tanstack/react-virtual.

Adds deps: dexie, @tanstack/react-virtual.

* feat(client): infinite-scroll pagination beyond the first 50 messages

The inbox previously loaded only the newest 50 messages per folder with no
way to see older mail. Adds cursor-based pagination on top of the
virtualized list:

- DataContext tracks a per-folder `before` UID cursor, `hasMore`, and
  `loadingMore`, and exposes loadMore(role). loadAll records the first
  page's cursor; loadMore fetches the next page (de-duped) and appends to
  state + IndexedDB cache.
- ThreadList auto-loads the next page when the last row scrolls into view
  (react-virtual), with a footer spinner while fetching.
- Inbox/Sent/Trash wire loadMore for their role. Pagination is suppressed
  while a search query is active (client-side search only filters loaded
  rows). The backend already supported the `before` cursor + next_before.

* feat: Gmail-style paged navigation ("1–50 of N") instead of infinite scroll

Replaces the append-on-scroll pager with classic page controls: a
"start–end of total" label and prev/next arrows above the list.

Backend:
- imap.ListMessages also returns the mailbox total (mbox.Messages);
  the messages endpoint includes it as `total` for the "of N" count.

Frontend:
- DataContext tracks page/total/pageLoading per folder plus a per-page
  `before` cursor history (ref), and exposes nextPage/prevPage that
  REPLACE the visible page (forward cursor discovered from next_before,
  back reuses the stored cursor). Only page 0 is mirrored to the cache.
- ThreadList renders the pager bar above the virtualized scroll area and
  resets scroll to top on page change.
- Inbox/Sent/Trash wire prev/next for their role; the pager is hidden
  while a search query is active (search filters the loaded page only).