Kerebrom v2.1.9

Kerebrom v2.1.9 is an SZ-5 iterative audit release focused on making first-time installs and Doctor verification line up cleanly.

Fixes:

• make install-user now delegates to the consent-aware installer, so missing or old Go fails with clear guidance instead of raw build errors.
• Doctor now checks the requested setup target, or only detected configs in auto/default mode, avoiding false WARNs for clients the user did not install.
• Doctor coverage now includes Gemini CLI, OpenCode, Cursor, Windsurf, and VS Code alongside Codex and Claude targets.

Verification:

• go test -count=1 ./...
• go test -count=1 -race ./...
• go vet ./...
• go build ./...
• go mod verify
• staticcheck ./...
• govulncheck ./...
• kerebrom doctor --deep
• Fresh HOME install simulations for auto and all, both Doctor PASS without WARN/FAIL.
• Missing Go and old Go simulations now produce actionable installer guidance.