Task #466: Clean notes page from email-like 4-tab bar

User asked to remove the prominent 4-tab bar (My Notes / Inbox / Sent /
Archive) from the notes page because it made the page feel like an email
client, and they rarely use the share-between-users feature.

Changes (artifacts/tx-os/src/pages/notes.tsx):
- Deleted the inline-flex TabButton row that held the four view tabs.
- Page now opens directly on the unified "active" feed.
- Added an overflow DropdownMenu (⋯ MoreVertical icon) on the end of the
  controls row containing three items: Inbox (with unread badge), Sent,
  Archived. Each item calls setView() with the same TabId values, so all
  downstream branching (data fetching, filtering, composer visibility,
  folder rail) is unchanged.
- Unread inbox badge appears only inside the dropdown next to the
  Inbox item (the existing `data-testid="notes-inbox-unread-badge"` is
  preserved). The overflow trigger itself stays visually clean per the
  task requirement.
- Added a small "← My Notes" back button (testid notes-back-to-active)
  that appears only when view !== "active" so the user can return after
  drilling into Inbox/Sent/Archived without a visible tab bar.
- Removed the now-unused TabButton component definition.

Tests (artifacts/tx-os/tests/notes-inbox.spec.mjs):
- Replaced the two notes-tab-received / notes-tab-sent clicks with the
  open-dropdown-then-select-item sequence using the new overflow testids.

Validation:
- pnpm tsc --noEmit passes for @workspace/tx-os.
- Architect review: no severe issues; layout, a11y, RTL, z-index, and
  state-reset behavior all noted as sound.
- The `test` workflow has pre-existing failures (executive-meetings PDF,
  notes-share, groups-crud) that are explicitly out of scope per the
  task description and tracked by other open follow-up tasks.

No backend, schema, API, or i18n JSON changes were needed: the file
uses inline t() defaults, and `notes.tabs.received/sent/archived` keys
are reused inside the dropdown.

artifacts/tx-os/src/pages/notes.tsx

@@ -556,17 +556,9 @@ export default function NotesPage() {
                 aria-label={t("common.more", "More")}
                 title={t("common.more", "More")}
                 data-testid="notes-overflow-menu-trigger"
-                className="relative p-2 rounded-lg border border-slate-300/60 bg-white/60 text-muted-foreground hover:text-foreground hover:bg-white transition-colors"
+                className="p-2 rounded-lg border border-slate-300/60 bg-white/60 text-muted-foreground hover:text-foreground hover:bg-white transition-colors"
               >
                 <MoreVertical size={16} />
-                {unreadInboxCount > 0 && view !== "received" && (
-                  <span
-                    className="absolute -top-1 -end-1 inline-flex items-center justify-center rounded-full bg-rose-500 text-white text-[10px] min-w-[18px] h-[18px] px-1"
-                    data-testid="notes-overflow-unread-dot"
-                  >
-                    {unreadInboxCount}
-                  </span>
-                )}
               </button>
             </DropdownMenuTrigger>
             <DropdownMenuContent align="end" className="min-w-[180px]">