[GFI] Add a `coco doctor` health-check command

Goal

Add a coco doctor health-check that diagnoses a Coco install and prints a clear pass/fail report. New users currently have no single command to confirm everything wired up correctly.

What it should check

• Required tools present: git, bash, python3 (and node for the npm CLI)
• Detected IDE/adapter (~/.claude, ~/.cursor, VS Code, Codex)
• Symlinks resolve (no dangling links into the repo)
• Installed bundles (gsd / brain / team / superintelligence) and their asset counts
• For Superintelligence: that SI commands were generated (per-team + meta)
• Installed version + whether an update is available (reuse scripts/check-update.sh)

Files involved

• scripts/doctor.sh (new), or a doctor subcommand in bin/coco.js
• Wire a mention into install.sh output and the README "Staying Current" section

Acceptance criteria

• bash scripts/doctor.sh (or coco doctor) prints a readable report with ✓/✗ per check
• Exit code non-zero when a hard requirement is missing
• Offline-safe; no telemetry
• CI passes (install script syntax check)

Hints

• Reuse the detection logic in install.sh (detect_adapter) and scripts/check-update.sh.

Start with install.sh's detect_adapter logic and scripts/check-update.sh, then compare scripts/doctor.sh with a doctor subcommand in bin/coco.js. Trace the existing install output and the README "Staying Current" section. Done means the command reports each check with ✓/✗, returns non-zero for missing hard requirements, remains offline-safe, and passes the install script syntax check in CI.