feat(chat): old-Dispatch composer layout — textarea + send + status bar

Restore the ergonomic composer from old Dispatch: an auto-resizing textarea
(1→7 lines) with a fixed-width Send button beside it, and a status bar BELOW
holding a status icon · context-window fill bar (escalating success/warning/
error color) · compact token count (current / limit · pct%).

The bar reuses the latest turn's contextSize as current usage and HARDCODES a
1,000,000-token window limit as a placeholder (real per-model limit is the next
backend ask). Absorbs the standalone ContextSizeBadge (removed). Pure helpers
computeContextUsage + formatCompactTokens added to core/metrics (tested).
540 tests green.

1 files changed, 0 insertions, 1 deletions

diff --git a/src/features/chat/index.ts b/src/features/chat/index.ts
index adfb670..18ed693 100644
--- a/src/features/chat/index.ts
+++ b/src/features/chat/index.ts
@@ -6,7 +6,6 @@ export type { ChatStore, ChatStoreDependencies } from "./store.svelte";
 export { createChatStore } from "./store.svelte";
 export { default as ChatView } from "./ui/ChatView.svelte";
 export { default as Composer } from "./ui/Composer.svelte";
-export { default as ContextSizeBadge } from "./ui/ContextSizeBadge.svelte";
 export { default as ModelSelector } from "./ui/ModelSelector.svelte";
 
 /** Public module manifest — aggregated by the shell's "Loaded Modules" view. */