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/0022_branch_refactor.sql

@@ -0,0 +1,4 @@
+-- Rename merge_target → branch on initiatives, add default_branch to projects
+ALTER TABLE `initiatives` RENAME COLUMN `merge_target` TO `branch`;
+--> statement-breakpoint
+ALTER TABLE `projects` ADD COLUMN `default_branch` TEXT NOT NULL DEFAULT 'main';