feat(golemcore/brain): support brain 1.0.3 api

[alexk-dev]

Summary

• Bump golemcore/brain plugin metadata to version 1.0.3, including registry latest and versions/1.0.3.yaml.
• Align the plugin with golemcore-brain origin/main at 51767e0ca9713e9419deb21acf991b0039ac8794 (feat(brain): harden RAG index for bot consumption).
• Switch search_pages to the unified POST /api/spaces/{space}/search API and support the current modes: auto, fts, and hybrid.
• Default omitted search_mode to auto, matching the Brain API behavior.
• Add get_search_status for GET /api/spaces/{space}/search/status so integrations can inspect index readiness, stale documents, and embedding readiness.
• Add operations for space/full reindex, section patching, wiki graph, top accessed pages, and atomic wiki transactions.
• Extend create/update page payloads with optional tags and summary frontmatter fields.
• Update intellisearch fallback to consume unified search hits and then hydrate matched pages.
• Cover the new search/status/reindex behavior and schema surface in tests.