fix(cli): route calibration and search dashboard commands

[rivet-ops]

Summary

• Route gbrain calibration through CLI-only dispatch.
• Route gbrain search modes|stats|tune through the search dashboard without shadowing ordinary keyword search.
• Ensure gbrain search modes --help prints dashboard help while gbrain search <query> --help still uses shared keyword-search help.
• Add CLI integration coverage for calibration and search help routing.

Verification

• git diff --check
• Static scan of added lines for secrets / shell injection / eval / SQL injection: no matches
• bun test test/cli.test.ts test/commands-search.test.ts test/search-mode.test.ts test/doctor-search-mode.test.ts --timeout 180000 — 87 pass / 0 fail
• bun run verify — pass
• Independent reviewer — pass; no security concerns or logic blockers

Notes

• No Steward/Hunting write-capable GBrain MCP access was enabled.
• No Brain promotion gates were bypassed.
• No canonical Current Truth changes were made.