fix(summary): normalize repeated valid citations

[rteoo]

Summary

• Automatic summaries rejected repeated valid segment IDs with the missing/invalid citations error, even though the native output schema permits repetitions. Normalize repeated citations in their original order while preserving unknown-ID rejection and existing input limits.
• Add regression coverage for single-chunk summaries, hierarchical reduction, and preservation of the prior report when any citation is unknown.

Testing

• Reproduced both duplicate-citation failures before the fix; both pass afterward.
• Focused intelligence, summary, and runtime tests: 58 passed.
• Full unittest suite: 1,193 tests run successfully, 12 skipped. The native capture helper is not built in the isolated checkout.
• Ruff 0.16.3 and Git whitespace checks passed.
• Manually reviewed the staged patch, outgoing commit, and noreply identities. Only synthetic fixtures are included; no standalone secret scanner was available.

Risks

• Unknown, empty, malformed, and oversized citation lists remain rejected; prior-result preservation remains intact.
• The original rejected model response was not logged. This fixes a reproduced cause of the reported error; live native-model generation and playback were not verified.