Mobile: indefinite phone-fit hold + configurable auto-restore

[Jinwoo-H]

Why

When the mobile app leaves a terminal (tab swap, app background, lock screen), the PTY currently restores to desktop dims ~300ms later. For TUI apps like Claude Code and codex this fires an expensive reflow that disrupts the on-screen UI even though the user is coming right back. Users want the terminal to stay at phone size, with an explicit way back to desktop.

What

• Default: indefinite hold. The phone-fit override and PTY dims stay put after the last mobile subscriber leaves. The 300ms debounced restore is gone.
• Escape hatch: the existing desktop banner is widened to also show when a terminal is held with no active mobile driver, with copy/button adapted ("This terminal is held at phone size... Restore"). Click Restore → PTY snaps back to desktop dims.
• Optional auto-restore: new mobileAutoRestoreFitMs setting on GlobalSettings (number | null). null = Indefinite. Finite values (clamped server-side to [5s, 60min]) schedule a wall-clock restore that long after the last unsubscribe.
• Settable from both ends: dropdown in desktop Mobile preferences (Indefinite / 1m / 5m / 30m) and a per-host expandable picker in the mobile Settings screen. Mobile uses two new RPCs on the existing terminal.* namespace: terminal.getAutoRestoreFit and terminal.setAutoRestoreFit.

See docs/mobile-fit-hold.md for the full design (3-iteration design review).

Notable runtime semantics

• reclaimTerminalForDesktop widened: handles both the active-subscriber path (existing) and the held-no-subscriber path (resolves restore target via the override's snapshotted baseline; applyLayout remains the sole writer of terminalFitOverrides).
• Setting transitions: finite → null cancels every pending restore timer; null → finite does NOT retroactively schedule timers for already-held PTYs (the new value applies to the next unsubscribe).
• Re-subscribe before a finite-window restore fires cancels the pending timer.

Tests

8 new tests in mobile-subscribe-integration.test.ts covering: indefinite hold, finite-delay auto-restore, re-subscribe-cancels, manual reclaim of held PTY, finite→null clears all timers, null→finite no retro-scheduling, and clamp behavior. Updated 2 mock stores (mobile-subscribe-integration, mobile-presence-lock) and 2 codex-accounts test fixtures for the new field. All 48 mobile-related tests pass; tc:node and tc:web clean.

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