fix(core): mirror summary thinking into reasoning events

[Alexxigang]

Summary

• mirror summary-phase ThinkingBlock chunks into ReasoningChunkEvent
• keep the existing SummaryChunkEvent behavior for summary streaming intact
• add regression tests for summary thinking delivery, accumulated reasoning content, and hook event order

Why this fix

ReActAgent uses a dedicated summary streaming path after max-iteration fallback. In that path, a streamed ThinkingBlock currently only triggers SummaryChunkEvent, even though the same provider/model behavior is exposed as ReasoningChunkEvent in normal reasoning streams.

That breaks the hook abstraction for clients that render reasoning exclusively from ReasoningChunkEvent, especially with models like qwen3.5-plus that may place thinking deltas inside the summary stream.

This patch keeps summary hooks working as before, while also mirroring summary-phase thinking chunks into ReasoningChunkEvent with accumulated thinking content.

Fixes #1152.

Validation

• mvn -pl :agentscope-core -am spotless:apply
• mvn -pl :agentscope-core -am "-Dtest=ReActAgentSummaryThinkingHookTest" test
• mvn -pl :agentscope-core -am "-Dtest=ReActAgentTest,ReActAgentThinkingCumulativeTest,ReActAgentSummaryThinkingHookTest" test

[Alexxigang]

Rebased this PR onto the current main and refreshed the head branch so it can be re-evaluated without the previous merge-conflict state.