feat(server): extend _meta.vouch_hot_memory to all read-side kb.* tools

[jsdevninja]

What changed

Every primary read-side kb.* tool now attaches _meta.vouch_hot_memory — a TTL-cached sidebar of recently approved claims — when the KB has recent activity. Coverage extends from kb.search / kb.context / kb.read_claim to kb.read_page, kb.read_entity, kb.read_relation, and all kb.list_* methods. kb.list_* responses are wrapped in {"items": [...], "_meta": {...}} with a deprecation note for clients that expected a flat list. kb.capabilities advertises the contract under hot_memory.

Closes #225

Why

Gbrain attaches its hot-memory sidebar to every MCP read response; vouch only covered three tools after the initial hot-memory work. Agents calling kb.read_entity or kb.list_pending had to make a second round-trip to learn what just changed. This is the cheap follow-up that fully closes that gap.

What might break

Breaking (JSONL / MCP): kb.list_pages, kb.list_claims, kb.list_entities, kb.list_relations, kb.list_sources, and kb.list_pending no longer return a bare list. They return a dict envelope with an items key. _meta.deprecation documents the migration (result.items instead of result). No on-disk .vouch/ layout changes; no new write paths; the review gate is untouched.

Non-breaking: Dict-returning read tools (kb.read_*, kb.search, kb.context) keep their existing top-level shape; _meta.vouch_hot_memory is additive and omitted when the sidebar would be empty.

VEP

Not required — read-side response decoration only; no object model, on-disk layout, bundle format, or audit-log shape changes.

Tests

• make check passes locally (lint + mypy + ruff)
• New / changed behaviour has a test (tests/test_hot_memory.py, including test_hot_memory_universal_coverage)
• CHANGELOG.md updated under ## [Unreleased]

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