What

Replace hardcoded empty-state suggestions in the chat sidebar with prompts derived from the user's actual memories.

Why

The old DEFAULT_SUGGESTIONS referenced content-specific strings like "My Gita" — a new user immediately sees prompts about content they don't own, which breaks trust before the first interaction. The emptyStateSuggestions prop on ChatSidebar already existed but was never sourced; this PR completes that.

How

• extractMemoryLabel + deriveSuggestionsFromMemories — pure helper functions, easily unit-testable
• useDynamicSuggestions hook — fetches up to 20 memories via POST /v3/documents/documents (scoped by containerTags) and returns suggestions with this fallback chain:
• Parent-supplied emptyStateSuggestions prop always wins and existing callers unaffected
• Skeleton loader at identical dimensions to prevent layout shift when suggestions swap in

Notes

• No new endpoints. Reuses the same route the memory grid calls.
• No LLM call in the generation path. Template-based; LLM-generated is a natural follow-up.
• Hook + helpers are decoupled from the sidebar UI, so they survive the upcoming chat refactor.