[P1] Extract dapp + app-opened metrics from `background.js`

**Parent Epic:** [#44543 — `app/scripts/background.js` decomposition](https://github.com/MetaMask/metamask-extension/issues/44543)
**File:** `app/scripts/background.js` → `app/scripts/lib/metrics/`
**Size:** M

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## Problem

`emitDappViewedMetricEvent`, `trackDappView`, `emitAppOpenedMetricEvent`, `shouldEmitAppOpened`, `trackAppOpened` (~1278–1435), and `onNavigateToTab` (~2273–2319) emit dapp/app-opened metrics and DeFi-referral navigation. They own the tab→origin registries `senderOriginMapping`/`tabOriginMapping`/`frameIdMapping` (confined to this cluster). `shouldEmitAppOpened` reads the shared UI-presence counters — the one cross-cluster read. Called from the connection cluster.

## Solution

`app/scripts/lib/metrics/dapp-metrics.ts`, injecting `getController()` + a single `isAnyUiOpen()` predicate. Extract `createUiPresenceTracker()` from the root as part of this ticket (the root keeps ownership of the counters; the module receives the predicate). The three origin registries move entirely into this module (self-owned state).

## Acceptance Criteria

- [ ] TS module owning the origin registries; `isAnyUiOpen()` presence seam extracted from the root.
- [ ] Originals deleted; unit tests against a mock controller.
- [ ] `DappViewed` / `AppOpened` / DeFi-referral parity in a dev build.

Start in app/scripts/background.js with emitDappViewedMetricEvent, trackDappView, emitAppOpenedMetricEvent, shouldEmitAppOpened, trackAppOpened, and onNavigateToTab, then compare the target app/scripts/lib/metrics/dapp-metrics.ts design. Extract createUiPresenceTracker while keeping the root's counters and move the origin registries into the module. Add unit tests with a mock controller and verify DappViewed, AppOpened, and DeFi-referral parity in a dev build.

Written by the indexing model from the issue text.