Prove the longpress request envelope with a worst-case ledger test #3326

Follow-up 2b from #2879 (step 1 landed in #2916).

Problem

The longpress envelope is the literal envelopeMs: 210_000 in packages/command-registry/src/registry.ts. It rests on a comment sum: Android helper install 30 s (HELPER_INSTALL_TIMEOUT_MS, packages/platform-android/src/touch-helper.ts), the 120 s hold cap, and 15 s helper overhead. The comment also names an unbounded "hand off a running snapshot helper" step and the selector-resolution capture. Nothing checks the sum. The hold cap is a bare literal in src/commands/interaction/runtime/gestures.ts (requireIntInRange(options.durationMs, 'durationMs', 0, 120_000)).

Required

• Apply the Prove request envelopes cover their worst-case work: fold ledger test, prepare handler margin, batch/replay follow-up #2879 ledger pattern to the Android cold-helper route with a 120 s hold: a fake tool seam advances a virtual clock by each call's timeout, and the test asserts elapsed + 30 s <= resolveCommandRequestTimeoutMs(resolveCommandTimeoutPolicy('longpress'), …).
• Replace the 120_000 literal with a named constant that both the validator and the scenario read.
• Prove or correct 210_000, and point its comment at the test instead of the hand sum.