docs: add spec for multi-theme synthesis support

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/superpowers/specs/2026-03-26-multi-theme-design.md

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+# Design: Multi-Theme Synthesis Support
+
+**Date**: 2026-03-26
+**Scope**: Allow users to create multiple themes, each with its own content settings and sources, generating syntheses per theme.
+
+---
+
+## Context
+
+Currently each user has a single theme with one set of categories. Users who follow multiple topics (e.g. AI + Cybersecurity) must choose one or regenerate with different settings. This feature adds support for multiple themes per user.
+
+---
+
+## 1. Data Model
+
+### New table: `themes`
+
+```sql
+CREATE TABLE themes (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    name TEXT NOT NULL,
+    theme TEXT NOT NULL,
+    categories JSONB NOT NULL DEFAULT '[]',
+    max_items_per_category INTEGER NOT NULL DEFAULT 4,
+    max_age_days INTEGER NOT NULL DEFAULT 7,
+    summary_length INTEGER NOT NULL DEFAULT 3,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+CREATE INDEX idx_themes_user_id ON themes(user_id);
+```
+
+### Modified table: `sources`
+
+Add `theme_id UUID REFERENCES themes(id) ON DELETE CASCADE`. Sources become per-theme.
+
+### Modified table: `syntheses`
+
+Add `theme_id UUID REFERENCES themes(id) ON DELETE SET NULL`. Links each synthesis to its theme. `SET NULL` preserves syntheses when a theme is deleted.
+
+### Modified table: `settings`
+
+Remove columns that move to `themes`: `theme`, `categories`, `max_items_per_category`, `max_age_days`, `summary_length`.
+
+### Migration strategy
+
+1. Create `themes` table
+2. For each user with settings, create a default theme from their current content settings
+3. Add `theme_id` to `sources`, populate with the user's default theme
+4. Add `theme_id` to `syntheses`, populate with the user's default theme
+5. Drop moved columns from `settings`
+
+---
+
+## 2. Backend API
+
+### New endpoints — Themes CRUD
+
+- `GET /api/v1/themes` — list user's themes
+- `POST /api/v1/themes` — create a new theme
+- `PUT /api/v1/themes/:id` — update a theme
+- `DELETE /api/v1/themes/:id` — delete a theme (syntheses kept with `theme_id = NULL`)
+
+### Modified endpoints
+
+- `GET /api/v1/sources` — add optional `?theme_id=` filter
+- `POST /api/v1/sources` — require `theme_id` in request body
+- `POST /api/v1/syntheses/generate` — require `theme_id` in request body
+- `GET /api/v1/syntheses` — response includes `theme_name`. Add optional `?sort=date|theme` param.
+
+### Pipeline change
+
+`run_generation_inner` receives `theme_id` and loads content settings (theme, categories, max_items, max_age, summary_length) from the `themes` table instead of `settings`. Global settings (provider, models, batch_size, rate limits, etc.) still come from `settings`.
+
+---
+
+## 3. Frontend — "Personnaliser les syntheses" page
+
+### Navigation rename
+
+"Sources personnalisees" → "Personnaliser les syntheses"
+
+### Page layout
+
+1. **Theme selector** — dropdown listing all user themes + "Creer un nouveau theme" button
+2. **Content settings** — theme name, search topic, categories (add/remove), max age, max items, summary length slider. Moved from Settings page.
+3. **Sources** — existing sources list, filtered by selected theme. Add/delete/bulk import scoped to current theme.
+4. **Delete theme** — danger button with confirmation.
+
+### Settings page changes
+
+Remove the "Contenu" section. Keep: Sources (pipeline tuning), Intelligence Artificielle, Performance, Import/Export.
+
+---
+
+## 4. Frontend — Home page enhancements
+
+- **Theme badge** on synthesis cards (below week label). "Theme supprime" for null theme_id.
+- **Sort toggle**: "Trier par: Date | Theme". Default: Date. Theme sort groups by theme name.
+- **Generate page**: theme dropdown before "Generate" button. Pre-selects last used theme.
+
+---
+
+## 5. Implementation phases
+
+| Phase | Scope | Dependencies |
+|-------|-------|-------------|
+| 1 | Data model + backend API (migrations, themes CRUD, pipeline) | None |
+| 2 | Theme management page (new page, move content settings) | Phase 1 |
+| 3 | Generation with theme (generate page dropdown) | Phase 1 |
+| 4 | Home page enhancements (theme badge, sort) | Phase 1 |
+
+Each phase produces working software. Phases 2-4 can be done in any order after Phase 1.
+
+---
+
+## Files overview
+
+### Phase 1 (Backend)
+- **Create:** `backend/migrations/20260326000028_create_themes.sql`
+- **Create:** `backend/src/db/themes.rs`
+- **Create:** `backend/src/models/theme.rs`
+- **Create:** `backend/src/handlers/themes.rs`
+- **Modify:** `backend/src/db/mod.rs`, `backend/src/models/mod.rs`, `backend/src/handlers/mod.rs`
+- **Modify:** `backend/src/router.rs` — add theme routes
+- **Modify:** `backend/src/db/sources.rs` — add `theme_id` filter
+- **Modify:** `backend/src/db/syntheses.rs` — add `theme_id`, `theme_name` to queries
+- **Modify:** `backend/src/models/settings.rs` — remove moved fields
+- **Modify:** `backend/src/db/settings.rs` — remove moved columns from queries
+- **Modify:** `backend/src/services/synthesis.rs` — load content settings from theme
+- **Modify:** `backend/src/handlers/generation.rs` — accept `theme_id`
+
+### Phase 2 (Theme page)
+- **Create:** `frontend/src/pages/ThemeManager.tsx`
+- **Create:** `frontend/src/api/themes.ts`
+- **Modify:** `frontend/src/App.tsx` — routes
+- **Modify:** `frontend/src/components/Navbar.tsx` — rename nav item
+- **Modify:** `frontend/src/pages/Settings.tsx` — remove Contenu section
+- **Modify:** `frontend/src/i18n/fr.ts` — labels
+
+### Phase 3 (Generate)
+- **Modify:** `frontend/src/pages/GenerateSynthesis.tsx` — theme dropdown
+- **Modify:** `frontend/src/api/syntheses.ts` — pass theme_id
+
+### Phase 4 (Home)
+- **Modify:** `frontend/src/pages/Home.tsx` — theme badge, sort
+- **Modify:** `frontend/src/types.ts` — add theme fields to types