feat: implement user activity stream and multiple API improvements

Activity Stream:
- Add UserActivity model with ActivityType enum to track user actions
- Create activity logging service with fire-and-forget pattern
- Add /api/user/activity endpoint with cursor pagination
- Add cleanup cron job for 90-day activity retention
- Integrate activity logging into 18 mutation API routes
- Add DashboardActivityStream component with virtualized rendering

API Improvements:
- Add distributed rate limiting via Vercel KV (with in-memory fallback)
- Add rate limiting to chat endpoint (30 req/min)
- Optimize BM25 search with database-level pre-filtering
- Fix JSON parse crash in search endpoint
- Add pagination to collection tools response (toolsLimit/toolsOffset)
- Add take limits to agent detail query to prevent excessive data fetch
- Fix hardcoded tool count calculation in agents dashboard

Schema Extraction:
- Add schemaExtractionAttemptAt and schemaExtractionError fields
- Separate rate limiting for failed (1 min) vs successful (1 hour) attempts
- Allow retry of failed extractions

Standardization:
- Create api-response.ts with standardized response helpers
- Add apiSuccess, apiError, apiNotFound, apiForbidden, etc.
- Update agents routes to use standardized format

Co-Authored-By: Claude <noreply@anthropic.com>

packages/db/prisma/schema.prisma

@@ -72,9 +72,11 @@ model Tool {
   aiAgent     Json?  @map("ai_agent") @db.JsonB // @deprecated - will be auto-extracted in future
 
   // Schema Extraction Fields
-  inputSchema       Json?     @map("input_schema") @db.JsonB // Full JSON Schema from executor
-  schemaSource      String?   @map("schema_source") @db.VarChar(20) // 'extracted' | 'author' | null
-  schemaExtractedAt DateTime? @map("schema_extracted_at")
+  inputSchema                Json?     @map("input_schema") @db.JsonB // Full JSON Schema from executor
+  schemaSource               String?   @map("schema_source") @db.VarChar(20) // 'extracted' | 'author' | null
+  schemaExtractedAt          DateTime? @map("schema_extracted_at") // Only updated on successful extraction
+  schemaExtractionAttemptAt  DateTime? @map("schema_extraction_attempt_at") // Updated on every attempt (for rate limiting)
+  schemaExtractionError      String?   @map("schema_extraction_error") @db.Text // Error message from last failed attempt
 
   // Tool Discovery Fields
   toolDiscoverySource String? @map("tool_discovery_source") @db.VarChar(20) // 'auto' | 'manual' | null
@@ -342,6 +344,7 @@ model User {
   toolLikes       ToolLike[]
   collectionLikes CollectionLike[]
   agentLikes      AgentLike[]
+  activities      UserActivity[]
 
   @@map("users")
 }
@@ -713,3 +716,62 @@ model AgentLike {
   @@index([userId])
   @@map("agent_likes")
 }
+
+// ============================================================================
+// Activity Stream Models
+// ============================================================================
+
+/// Activity type enum - types of user activities tracked
+enum ActivityType {
+  AGENT_CREATED
+  AGENT_UPDATED
+  AGENT_DELETED
+  AGENT_TOOL_ADDED
+  AGENT_TOOL_REMOVED
+  AGENT_COLLECTION_ADDED
+  AGENT_COLLECTION_REMOVED
+  COLLECTION_CREATED
+  COLLECTION_UPDATED
+  COLLECTION_DELETED
+  COLLECTION_TOOL_ADDED
+  COLLECTION_TOOL_REMOVED
+  TOOL_LIKED
+  TOOL_UNLIKED
+  COLLECTION_LIKED
+  COLLECTION_UNLIKED
+  AGENT_LIKED
+  AGENT_UNLIKED
+}
+
+/// UserActivity - tracks user actions for activity stream
+model UserActivity {
+  id           String       @id @default(cuid())
+
+  // Owner relationship
+  userId       String       @map("user_id")
+  user         User         @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  // Activity type
+  type         ActivityType
+
+  // Optional entity references (for linking to entities if they still exist)
+  agentId      String?      @map("agent_id")
+  collectionId String?      @map("collection_id")
+  toolId       String?      @map("tool_id")
+
+  // Denormalized fields (stored at creation time for display even after entity deletion)
+  targetName   String       @map("target_name") @db.VarChar(200)
+  targetType   String       @map("target_type") @db.VarChar(50) // 'agent' | 'collection' | 'tool'
+
+  // Additional context (e.g., toolName when adding to collection)
+  metadata     Json?        @db.JsonB
+
+  // Timestamps
+  createdAt    DateTime     @default(now()) @map("created_at")
+
+  @@index([userId])
+  @@index([userId, createdAt])
+  @@index([type])
+  @@index([createdAt])
+  @@map("user_activities")
+}