v1.11.5: ContextBar inline next to agent picker; remove ChatContextPopover

ContextBar relocated from a dedicated row above MessageList to inline with
the agent-picker row, filling the space to the right of the picker + plus
button. Always-visible (zero-state when no assistant message has run yet)
via chat.model_context_limit, which GET /api/sessions/:id/chats now
populates from a single getModelContext lookup per session.

ChatContextPopover above the input is removed entirely along with its
useChatContextStats hook (no remaining callers). Color tiers and the
auto-compaction threshold tooltip unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/api/types.ts

@@ -80,6 +80,12 @@ export interface Chat {
   message_count?: number;
   last_message_preview?: string | null;
   effective_context_tokens?: number | null;
+  // v1.11.5: model's full context window from llama-swap /props. Used by
+  // ContextBar to render the zero-state + auto-compaction threshold tooltip
+  // before any assistant message exists in the chat. null when upstream
+  // lookup failed (model unknown, llama-swap unreachable) — UI degrades
+  // to a "model context unknown" placeholder.
+  model_context_limit?: number | null;
 }
 
 export type MessageRole = 'user' | 'assistant' | 'tool' | 'system';