feat(api): add source management endpoints (Sprint 2)

Implement Sprint 2: Source Management

- Add SourceService with create, list, delete, research methods
- Add POST /api/v1/notebooks/{id}/sources - Add source (URL, YouTube, Drive)
- Add GET /api/v1/notebooks/{id}/sources - List sources with filtering
- Add DELETE /api/v1/notebooks/{id}/sources/{source_id} - Delete source
- Add POST /api/v1/notebooks/{id}/sources/research - Web research
- Add ResearchRequest model for research parameters
- Integrate sources router with main app

Endpoints:
- POST /sources - 201 Created
- GET /sources - 200 OK with pagination
- DELETE /sources/{id} - 204 No Content
- POST /sources/research - 202 Accepted

Technical:
- Support for url, youtube, drive source types
- Filtering by source_type and status
- Validation for research mode (fast/deep)
- Error handling with standardized responses

Related: Sprint 2 - Source Management

prompts/2-source-management.md

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+# Prompt Sprint 2 - Source Management
+
+## 🎯 Sprint 2: Source Management
+
+**Iniziato**: 2026-04-06  
+**Stato**: 🟡 In Progress  
+**Assegnato**: @sprint-lead
+
+---
+
+## 📋 Obiettivo
+
+Implementare la gestione delle fonti (sources) per i notebook, permettendo agli utenti di aggiungere URL, PDF, YouTube, Google Drive e avviare ricerche web.
+
+---
+
+## 🏗️ Architettura
+
+### Pattern da seguire (stesso di Sprint 1)
+
+```
+API Layer (FastAPI Routes)
+    ↓
+Service Layer (SourceService)
+    ↓
+External Layer (notebooklm-py client)
+```
+
+### Endpoints da implementare
+
+1. **POST /api/v1/notebooks/{id}/sources** - Aggiungere fonte
+2. **GET /api/v1/notebooks/{id}/sources** - Listare fonti
+3. **DELETE /api/v1/notebooks/{id}/sources/{source_id}** - Rimuovere fonte
+4. **GET /api/v1/notebooks/{id}/sources/{source_id}/fulltext** - Ottenere testo
+5. **POST /api/v1/notebooks/{id}/sources/research** - Ricerca web
+
+---
+
+## 📊 Task Breakdown Sprint 2
+
+### Fase 1: Specifiche
+- [ ] SPEC-004: Analisi requisiti Source Management
+- [ ] SPEC-005: Definire modelli dati fonti
+
+### Fase 2: API Design
+- [ ] API-003: Modelli Pydantic (SourceCreate, Source, ecc.)
+- [ ] API-004: Documentazione endpoints
+
+### Fase 3: Implementazione
+- [ ] DEV-007: SourceService
+- [ ] DEV-008: POST /sources
+- [ ] DEV-009: GET /sources
+- [ ] DEV-010: DELETE /sources/{id}
+- [ ] DEV-011: POST /sources/research
+
+### Fase 4: Testing
+- [ ] TEST-004: Unit tests SourceService
+- [ ] TEST-005: Integration tests
+
+---
+
+## 🔧 Implementazione
+
+### Tipi di Fonti Supportate
+
+```python
+class SourceType(str, Enum):
+    URL = "url"
+    FILE = "file"  # PDF, DOC, etc.
+    YOUTUBE = "youtube"
+    DRIVE = "drive"
+```
+
+### SourceService Methods
+
+```python
+class SourceService:
+    async def create(notebook_id: UUID, data: dict) -> Source
+    async def list(notebook_id: UUID) -> list[Source]
+    async def get(notebook_id: UUID, source_id: str) -> Source
+    async def delete(notebook_id: UUID, source_id: str) -> None
+    async def get_fulltext(notebook_id: UUID, source_id: str) -> str
+    async def research(notebook_id: UUID, query: str, mode: str) -> ResearchResult
+```
+
+---
+
+## 📝 Note Importanti
+
+1. **Riusare pattern Sprint 1**: Stessa struttura NotebookService
+2. **Gestione upload file**: Supportare multipart/form-data per PDF
+3. **Ricerca web**: Integrare con notebooklm-py research
+4. **Error handling**: Fonte già esistente, formato non supportato
+
+---
+
+## 🚀 Prossimi Passi
+
+1. @sprint-lead: Attivare @api-designer per API-003
+2. @api-designer: Definire modelli Pydantic
+3. @tdd-developer: Iniziare implementazione SourceService
+
+---
+
+**Dipende da**: Sprint 1 (Notebook CRUD) ✅  
+**Blocca**: Sprint 3 (Chat) 🔴