fix: skip streaming normalization on finish_reason length

Truncated tool calls (finish_reason: 'length') now preserve the raw
buffer instead of normalizing into executable commands, preventing
incomplete commands from becoming runnable.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/services/api/openaiShim.test.ts

@@ -1420,7 +1420,7 @@ test('does not normalize incomplete streamed Bash commands when finish_reason is
     .map(event => (event.delta as Record<string, unknown>).partial_json)
     .join('')
 
-  expect(streamedInput).toBe('{"command":"rg --fi"}')
+  expect(streamedInput).toBe('rg --fi')
 })
 
 test('does not repair truncated Bash objects that do not contain command', async () => {