Native AI theme editor on /sites/[id] (feature 3/3)

[gndclouds]

Summary

Promotes the existing Anthropic-backed theme generator — which today only runs once during admin site creation — into a first-class native editor on every site's settings page. Owners can describe the look they want, the model returns a cohesive color + font palette, the tokens are written to the site, and a rebuild is queued automatically.

This is feature 3 of 3 from `docs/features.md`. Template consolidation is intentionally not in this PR (per the decision to skip archiving for now); only the AI editor ships here.

This PR does not depend on PRs 1 / 2 — it branches straight off main and can ship independently.

What changed

• `src/app/api/sites/[id]/theme/ai/route.ts` — new owner-scoped POST. Reuses `generateAiSiteTheme()` and applies the same plan gate as the existing `/theme` PUT (admin / friend / pro / studio). With `apply: true` (default) it writes `themeColors` + `themeFonts` and queues `buildSite(id)` via `after()`.
• `src/components/site-ai-theme-box.tsx` — prompt textarea + Apply button, inline error / "Applied · rebuild queued" feedback, and per-browser prompt history in localStorage (top 8). Clicking a previous prompt drops it back into the textarea for iteration ("the same, but darker").
• `src/app/sites/[id]/page.tsx` — drops the AI box above the existing `theme.css` / `styles.css` editor on the Theme tab, so users can describe a vibe and then nudge the result by hand without leaving the page.

Why this shape

• `docs/features.md` lists a "prompt history" question; this PR resolves it lightweight (per-browser localStorage) rather than adding a `themePromptHistory` JSON column. Easy to migrate to the DB later when it earns a feature.
• Cost guardrail question is resolved by the plan gate — only paid plans (or admin/friend) reach the endpoint.
• The AI does NOT propose custom CSS to end users in this PR (`generateAiSiteTheme` still returns it, but the editor surfaces only colors + fonts). Custom CSS is editable in the dedicated `styles.css` tab.

Test plan

• As a Pro user, open the Theme tab on a site; AI box renders above the existing editor.
• Type a vibe ("warm, serif, mid-century book"), click Apply → API returns 200, site updates, rebuild queued, theme.css editor below picks up the new values.
• As a free user, AI box renders the upgrade hint instead of the input.
• Without `ANTHROPIC_API_KEY`, endpoint returns 503 with `ai_unconfigured` — error shows inline in the box.
• After applying, refresh the page: prompt history still listed; clicking an old prompt repopulates the textarea.

Open follow-ups (not in this PR)

• Template consolidation (kept out per scoping decision).
• Persisting prompt history on the site row in the DB so it follows the user across browsers.
• Diff-mode AI prompts ("only change the body font").

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Project	Deployment	Actions	Updated (UTC)
tiny-garden	Ready	Preview, Comment	May 11, 2026 8:28pm

[gndclouds]

📝 Changed routes:

/sites/[id]
(view full size)

Commit c0a3138 (https://tiny-garden-58wk9rv8s-tiny-factories.vercel.app).