feat: add model usage statistics tracking with heatmap and CSV export

drizzle/0007_add_model_usage.sql

@@ -0,0 +1,27 @@
+-- Model usage tracking table
+-- Records token usage for each Claude API call
+CREATE TABLE `model_usage` (
+	`id` text PRIMARY KEY NOT NULL,
+	`sub_chat_id` text NOT NULL REFERENCES `sub_chats`(`id`) ON DELETE CASCADE,
+	`chat_id` text NOT NULL REFERENCES `chats`(`id`) ON DELETE CASCADE,
+	`project_id` text NOT NULL REFERENCES `projects`(`id`) ON DELETE CASCADE,
+	`model` text NOT NULL,
+	`input_tokens` integer NOT NULL DEFAULT 0,
+	`output_tokens` integer NOT NULL DEFAULT 0,
+	`total_tokens` integer NOT NULL DEFAULT 0,
+	`cost_usd` text,
+	`session_id` text,
+	`message_uuid` text,
+	`mode` text,
+	`duration_ms` integer,
+	`created_at` integer
+);--> statement-breakpoint
+
+-- Indexes for query optimization
+CREATE INDEX `model_usage_created_at_idx` ON `model_usage` (`created_at`);--> statement-breakpoint
+CREATE INDEX `model_usage_model_idx` ON `model_usage` (`model`);--> statement-breakpoint
+CREATE INDEX `model_usage_project_id_idx` ON `model_usage` (`project_id`);--> statement-breakpoint
+CREATE INDEX `model_usage_chat_id_idx` ON `model_usage` (`chat_id`);--> statement-breakpoint
+CREATE INDEX `model_usage_sub_chat_id_idx` ON `model_usage` (`sub_chat_id`);--> statement-breakpoint
+-- Unique index for deduplication by message UUID
+CREATE UNIQUE INDEX `model_usage_message_uuid_idx` ON `model_usage` (`message_uuid`);

drizzle/0007_watery_winter_soldier.sql

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+CREATE TABLE `model_usage` (
+	`id` text PRIMARY KEY NOT NULL,
+	`sub_chat_id` text NOT NULL,
+	`chat_id` text NOT NULL,
+	`project_id` text NOT NULL,
+	`model` text NOT NULL,
+	`input_tokens` integer DEFAULT 0 NOT NULL,
+	`output_tokens` integer DEFAULT 0 NOT NULL,
+	`total_tokens` integer DEFAULT 0 NOT NULL,
+	`cost_usd` text,
+	`session_id` text,
+	`message_uuid` text,
+	`mode` text,
+	`duration_ms` integer,
+	`created_at` integer,
+	FOREIGN KEY (`sub_chat_id`) REFERENCES `sub_chats`(`id`) ON UPDATE no action ON DELETE cascade,
+	FOREIGN KEY (`chat_id`) REFERENCES `chats`(`id`) ON UPDATE no action ON DELETE cascade,
+	FOREIGN KEY (`project_id`) REFERENCES `projects`(`id`) ON UPDATE no action ON DELETE cascade
+);