fix: resolve all ESLint errors blocking CI releases

- Extract ThemeContext and ToolCollapseContext definitions into separate
  files to satisfy react-refresh/only-export-components rule
- Move useTheme and useToolCollapse hooks to dedicated hook files
- Fix empty catch block in ThemeContext (add comment)
- Replace Date.now() ref in ThinkingIndicator with useState initializer
- Update all imports across components

Closes feedback #58

src/hooks/useTheme.ts

@@ -0,0 +1,4 @@
+import { useContext } from 'react';
+import { ThemeContext } from '../contexts/ThemeContextDef';
+
+export const useTheme = () => useContext(ThemeContext);

src/hooks/useToolCollapse.ts

@@ -0,0 +1,6 @@
+import { useContext } from 'react';
+import { ToolCollapseContext } from '../contexts/ToolCollapseContextDef';
+
+export function useToolCollapse() {
+  return useContext(ToolCollapseContext);
+}