Align support KB installer with Eva Brain source-scoped updates

[100yenadmin]

Summary

Eva Brain's v0.28 catch-up PR exposed that the support KB repo still has installer/update assumptions that are now stale for the fleet-safe Eva Brain install path.

Current issues

• scripts/update-client.mjs still runs a bare gbrain embed --stale after named-source sync. On current Eva Brain installs this should be source-scoped when named sources are available: gbrain embed --stale --source openclaw-support-kb.
• Published docs/scripts still reference the old 100yenadmin/openclaw-support-kb ownership as canonical. We need to decide and encode the current canonical public repo path for Electric Sheep installs.
• Install examples assume $HOME/.gbrain/... directly and need a clearer GBRAIN_HOME/fleet-home isolation contract so customer VMs and temp canaries do not accidentally write to the operator's live home.

Acceptance criteria

• Agent install/update path uses named-source sync and source-scoped stale embedding where supported.
• Legacy fallback remains explicit and only used for older GBrain versions that lack named sources.
• Repo URL/default ownership is updated or intentionally documented with the current canonical decision.
• Install/status tests cover custom GBRAIN_HOME, custom OPENCLAW_SUPPORT_KB_DIR, and custom OPENCLAW_SKILLS_DIR.
• README and INSTALL_FOR_AGENTS.md match the command behavior.

Evidence

Eva Brain temp canary can import/search the KB cleanly with no embeddings:

• 653 markdown files imported
• 3054 chunks created
• 0 import errors
• search found Telegram Setup And Repair
• gbrain doctor --json returned health score 95 with no warnings

This issue is for packaging/update safety, not KB content quality.