refactor: Remove unused ContextState interface

ContextState was defined but never used - it was a redundant
subset of ContextHealth.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tui/src/lib/types.ts

@@ -45,13 +45,6 @@ export interface AgentEntry {
   tools: ToolEntry[];
 }
 
-export interface ContextState {
-  tokens: number;
-  percent: number;
-  remaining: number;
-  maxTokens: number;
-}
-
 export interface ContextHealth {
   tokens: number;
   percent: number;