refactor: Co-locate server artifacts under apps/server/

Move drizzle/, dist/, and coverage/ into apps/server/ so all
server-specific artifacts live alongside the source they belong to.

- git mv drizzle/ → apps/server/drizzle/
- drizzle.config.ts: out → ./apps/server/drizzle
- tsconfig.json: outDir → ./apps/server/dist, exclude drizzle dir
- package.json: main/bin/clean point to apps/server/dist/
- vitest.config.ts: reportsDirectory → ./apps/server/coverage
- .gitignore: add coverage/ entry
- ensure-schema.ts: update getMigrationsPath() for new layout
- docs/database-migrations.md: update drizzle/ references

apps/server/drizzle/0007_robust_the_watchers.sql

@@ -0,0 +1,27 @@
+PRAGMA foreign_keys=OFF;--> statement-breakpoint
+CREATE TABLE `__new_tasks` (
+	`id` text PRIMARY KEY NOT NULL,
+	`plan_id` text,
+	`phase_id` text,
+	`initiative_id` text,
+	`name` text NOT NULL,
+	`description` text,
+	`type` text DEFAULT 'auto' NOT NULL,
+	`category` text DEFAULT 'execute' NOT NULL,
+	`priority` text DEFAULT 'medium' NOT NULL,
+	`status` text DEFAULT 'pending' NOT NULL,
+	`requires_approval` integer,
+	`order` integer DEFAULT 0 NOT NULL,
+	`created_at` integer NOT NULL,
+	`updated_at` integer NOT NULL,
+	FOREIGN KEY (`plan_id`) REFERENCES `plans`(`id`) ON UPDATE no action ON DELETE cascade,
+	FOREIGN KEY (`phase_id`) REFERENCES `phases`(`id`) ON UPDATE no action ON DELETE cascade,
+	FOREIGN KEY (`initiative_id`) REFERENCES `initiatives`(`id`) ON UPDATE no action ON DELETE cascade
+);
+--> statement-breakpoint
+INSERT INTO `__new_tasks`("id", "plan_id", "phase_id", "initiative_id", "name", "description", "type", "category", "priority", "status", "requires_approval", "order", "created_at", "updated_at") SELECT "id", "plan_id", NULL, NULL, "name", "description", "type", 'execute', "priority", "status", NULL, "order", "created_at", "updated_at" FROM `tasks`;--> statement-breakpoint
+DROP TABLE `tasks`;--> statement-breakpoint
+ALTER TABLE `__new_tasks` RENAME TO `tasks`;--> statement-breakpoint
+PRAGMA foreign_keys=ON;--> statement-breakpoint
+ALTER TABLE `initiatives` ADD `merge_requires_approval` integer DEFAULT true NOT NULL;--> statement-breakpoint
+ALTER TABLE `initiatives` ADD `merge_target` text;