feat(tui): first-class onboarding flow within sciclaw tui

[drpedapati]

Goal

Make sciclaw tui the single entry point for new users. After brew install sciclaw, a non-technical user should complete the full setup without leaving the TUI.

Approach: guided wizard (first run) + capable tabs (repeat)

First-run wizard (Home tab overlay)

When TUI launches with no config file, the Home tab shows a guided setup wizard overlay:

1. Welcome — "sciClaw setup — this takes about 2 minutes"
2. Config creation — auto-creates ~/.picoclaw/config.json with defaults
3. Authentication — "Choose your AI provider" → spawns OAuth device code flow
4. Smoke test (optional) — one-shot agent message, shows pass/fail
5. Chat channel — [t] Telegram / [d] Discord / [s] Skip
6. Gateway service — auto-installs and starts background service
7. Done — shows all-green checklist, Enter dismisses

Idempotency: Wizard only appears when config is missing. If config exists but other pieces are incomplete, Home tab's existing SuggestedStep() + Enter→navigate handles it.

Tab enhancements (for repeat/power users)

Tab	Addition
Home	Enter on SuggestedStep → auto-navigate to target tab
Home	[t] Test connection smoke test
Settings	Config bootstrap if missing, PubMed API key text field
Skills	[I] Install baseline skills when list is sparse

Files

• cmd/picoclaw/tui/tab_home.go — wizard overlay, Enter→navigate, smoke test
• cmd/picoclaw/tui/tab_settings.go — config bootstrap, PubMed key field
• cmd/picoclaw/tui/tab_skills.go — baseline skills install button
• cmd/picoclaw/tui/model.go — homeNavigateMsg handler
• cmd/picoclaw/tui/snapshot.go — ConfigExists field, workspace auto-creation

Acceptance

• Fresh install: sciclaw tui with no config → guided wizard appears
• Wizard walks through: config → auth → smoke test → channel → service
• Wizard is idempotent — re-running TUI after setup shows normal Home (no wizard)
• Enter on SuggestedStep navigates to correct tab for repeat users
• Skills [I] installs baseline skills with progress
• Settings shows PubMed API key field
• Home [t] runs smoke test
• Full flow: fresh install → all-green checklist without leaving TUI