fix(compaction): do not forward agent tools to summarization

[leeseunguk]

Summary

Summarization copied the live agent tool list into the summarizer request. Tool-preferring models (observed: openai-codex/gpt-5.6-sol) then ended the summary with stopReason: toolUse and no text. senpi treats that as empty-summary, rejects compaction, and leaves the session above the threshold.

This makes getSummarizationTools() return []. Summarization is a prose-only call.

Fixes #1067

Test plan

• bun test test/compaction/summarization-no-tools.test.ts
• Reproduce: compact a large session on a tool-preferring model; summarizer must not emit stopReason: toolUse / empty-summary.

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Summary by cubic

Prevents tool-only summaries during compaction by not forwarding agent tools to the summarizer. Previously we copied the live tool list; now getSummarizationTools() returns [], so tool‑preferring models no longer stop with toolUse and empty text, and compaction can proceed.

• Replaces inline tool forwarding with compactionSummarizationTools() that always returns [] and wires it into getSummarizationTools().
• Adds a unit test ensuring no tools are forwarded even when the live list is non‑empty, and documents the change in changes.md.

^{Written for commit 35d9f06. Summary will update on new commits.}