fix(web): normalize Windows drive letter case for session path matching (#675)

On Windows, VS Code's uri.fsPath returns a lowercase drive letter
(e.g. d:\MyProject) while the OpenCode server stores paths using
process.cwd() which returns uppercase (D:\MyProject). This caused
session queries to return empty results due to case-sensitive string
comparison.

Normalize drive letters to uppercase in both the VS Code extension
(opencode.ts) and the shared UI client (client.ts) so that directory
paths match regardless of the source casing.

Fixes #670

packages/ui/src/lib/opencode/client.ts

@@ -199,7 +199,11 @@ class OpencodeService {
       return null;
     }
 
-    const normalized = trimmed.replace(/\\/g, '/');
+    // Normalize backslashes and uppercase the Windows drive letter so that
+    // d:\MyProject and D:\MyProject resolve to the same canonical form.
+    const normalized = trimmed
+      .replace(/\\/g, '/')
+      .replace(/^([a-z]):/, (_, letter: string) => letter.toUpperCase() + ':');
     const withoutTrailingSlash = normalized.length > 1 ? normalized.replace(/\/+$/, '') : normalized;
 
     return withoutTrailingSlash || null;