Add Power Saving settings to settings search

[gildor]

Problem

The Power Saving (lite mode) screen is not in the settings search index. settingsSearchableItems builds the index from explicit per-section lists (profile, stickers, notifications, privacy, data, proxy, appearance, language), and no list was ever added for lite mode when it shipped.

The practical effect: searching Settings for emoji, animation, sticker animation or power returns nothing for these toggles. Since the screen is named after a motivation (saving battery) rather than what it controls (looping emoji, stickers, GIFs, videos, blur, menu animations), a user who wants to stop animated emoji from looping has no path to it except already knowing it lives under General.

This is easy to hit in practice — the toggle people usually want is Emoji Animations, and search is the natural way to look for it.

Change

Adds powerSavingSearchableItems, indexing:

• the screen itself, under its existing title GeneralSettings.LiteMode, breadcrumb General
• every toggle in LiteMode.allKeys, using each key's existing .title, breadcrumbs General › Power Saving Mode

Each key's .info text is passed as alternate, so the descriptions already shown on the rows become searchable too — e.g. "Loop animated emoji in messages, reactions and statuses" makes loop, reactions and statuses find the Emoji Animations toggle.

All items push LiteModeController. There is no item-tag/focus mechanism on that controller, so sub-items open the screen rather than scrolling to a specific row, matching how the language and sticker items behave.

Supporting changes:

• new .powerSaving case in SettingsSearchableItemIcon (reuses theme.icons.settingsGeneral) and in SettingsSearchableItemId (namespace 16, appended so existing persisted recent-search indices keep their meaning)
• extension LiteModeKey in LiteModeController.swift is no longer private, so the search items reuse the exact strings the rows render

No new localized strings — everything reuses keys that already exist.

Notes

Synonyms are deliberately not added. Words like "battery" would need new SettingsSearch.Synonyms.* entries, which go through the translations platform; happy to add them in a follow-up if you'd like.

Verified by inspection and swiftc -parse; I wasn't set up to run a full Xcode build locally, so please give it a compile before merging.

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