feat(livetv): add guide search with jump-to-channel/program

[l3gitpanda]

What

Adds a search to the Live TV guide: a search icon on the Guide tab opens a sheet that filters channels (name, call sign, number) and programs airing in the next 24 hours (title / series name) as you type. Selecting a result closes the sheet and jumps to it in the guide — shifting the guide's time window when the airing isn't in the current one, scrolling to the channel row, and landing d-pad focus on the matched program block.

Screenshots

How

• New GuideSearchSheet modeled on the existing subtitle-language filter sheet (FocusableTextField + in-memory filter + FocusableListTile rows), shown via OverlaySheetController.showAdaptive like the reorder-favorites sheet. Programs come from one fetchSchedule(now, now+24h) fan-out over liveTvServers when the sheet opens; each program's channel is resolved once so keystroke filtering stays cheap.
• Two new public methods on GuideTabState (jumpToChannel / jumpToProgram) reuse the existing day/time-picker window mechanics, _scrollToChannel / _scrollToProgramTime, and the focusContent() keyboard-mode gating.
• Companion remote: while the sheet is open it takes over CompanionRemoteReceiver.onSearchAction (same save/restore idiom as the video player's overrides) so a query typed on the phone lands in the guide search with the TV keyboard dismissed; the global Search tab handler is restored on close. No protocol changes.
• Searching covers all channels; jumping to a non-favorite while the favorites filter is on drops the filter so the target row exists.
• 5 new i18n strings (base locale only, fallback_strategy: base_locale).

Testing

• flutter analyze clean; dart format (120) applied.
• Manually verified on Windows desktop and TV (d-pad): filter/jump for channels and programs incl. window shift for later airings, OSK focus flow, companion-remote query submit into the open sheet, and restore of global search after closing.

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