feat(claude-agent-sdk): surface raw MCP tool name via metadata

[boyuan-fh]

Fixes #2633

Problem

stripMcpPrefix removes the mcp__<server>__ prefix from tool names before
the adapter emits TOOL_CALL_START events and before it builds assistant
message tool calls. This makes built-in and MCP tool calls indistinguishable
in the event stream and message history.

Changes (integration package only -- no @ag-ui/core change)

• Emit metadata: { rawName } on TOOL_CALL_START in both the streaming path
  (adapter.ts) and the non-streaming path (handlers.ts), carrying the raw
  prefixed name while toolCallName stays the stripped display name.
• Carry metadata: { rawName } on tool calls built by buildAguiAssistantMessage
  (utils.ts) and on the in-flight message accumulator (adapter.ts).
• For built-in tools, metadata.rawName equals the display name.

The raw name uses the metadata map that both BaseEventSchema (events) and
ToolCallSchema (messages) already declare, so no shared-schema edit is
required and the field survives .parse() on both surfaces.

Tests (new adapter.raw-tool-name.test.ts + schema-survival.test.ts)

• MCP tool emits metadata.rawName with the full prefix on the streaming path;
  built-in tool emits metadata.rawName equal to the display name.
• Non-streaming (complete assistant message) path emits metadata.rawName.
• MCP and built-in tool calls in MESSAGES_SNAPSHOT carry metadata.rawName.
• schema-survival.test.ts parses through the real ToolCallStartEventSchema
  and ToolCallSchema from @ag-ui/core and asserts metadata.rawName
  survives .parse() on both -- proving the design premise against the real
  schemas rather than a mock.