docs: add model split implementation plan

docs/superpowers/plans/2026-03-25-model-split.md

@@ -0,0 +1,41 @@
+# Model Split — Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Rename ai_model_writing → ai_model_websearch, split provider models into scraping and websearch lists with GPT-5 generation models.
+
+**Architecture:** Rename DB column, split JSONB `models` into `models_scraping` + `models_websearch`, update all backend structs/queries/handlers + frontend types/dropdowns.
+
+**Tech Stack:** Rust (sqlx), SolidJS, PostgreSQL
+
+**Spec:** `docs/superpowers/specs/2026-03-25-model-split-design.md`
+
+---
+
+### Task 1: Migration — rename column + restructure JSONB
+
+**Files:**
+- Create: `backend/migrations/20260325000019_model_split.sql`
+- Modify: `CLAUDE.md`
+
+The migration:
+1. Renames `ai_model_writing` → `ai_model_websearch` in settings
+2. Renames `models` → `models_scraping` in admin_providers JSONB
+3. Copies `models_scraping` → `models_websearch` (same models initially for Gemini/Anthropic)
+4. Updates OpenAI specifically with GPT-5 model lists
+
+### Task 2: Backend model + DB changes
+
+Update all Rust structs and DB queries for the rename and new JSONB structure.
+
+### Task 3: Pipeline + handlers
+
+Update synthesis.rs, config handler, admin handler.
+
+### Task 4: Frontend
+
+Update types, Settings dropdowns, i18n, E2E test.
+
+---
+
+These 4 tasks are tightly coupled — I'll execute them as 2 subagent calls (backend + frontend).