#7528: feat: Adds slash command suggestions to chat

Implements slash command suggestions in the chat input, showing available commands as the user types. Adds command history navigation using arrow keys for quick access to previous commands. AI: Assisted Development Testing: Unit test Added and Tested in live environment build. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Adds chat slash-command suggestions UI (new command registry + dropdown styling) and introduces command history persistence in UI settings, with ArrowUp/ArrowDown navigation in the chat textarea. Changes flow through the existing `OpenClawApp` state → `renderApp` → `renderChat` props pipeline: `UiSettings.chatCommandHistory` is loaded from localStorage, exposed on `AppViewState`, and then used by `ui/src/ui/views/chat.ts` to render suggestions and implement history navigation while composing. <h3>Confidence Score: 3/5</h3> - Generally safe to merge, with a few UX/accessibility pitfalls worth fixing before shipping broadly. - Changes are localized to the UI chat view and settings persistence, and the logic is straightforward. Main concerns are user-facing behavior issues (suggestions disappearing when arguments are typed, history navigation clobbering drafts / stealing caret movement) and some minor robustness/a11y semantics gaps. I couldn’t run tests in this environment (no node/pnpm), so confidence is moderate. - ui/src/ui/views/chat.ts (history navigation + suggestion behavior); ui/src/ui/app-chat.ts (history write timing); ui/src/ui/storage.ts (settings validation) <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->