fix: unify data directory for dev and prod environments (#116)

Add DATA_DIR env var support to configure the data directory path.
All hardcoded resolve(cwd, 'data') paths now use a central getDataDir()
function from db-utils.ts that checks DATA_DIR first, falling back to
resolve(cwd, 'data').

This prevents local dev (cd backend && npm run dev) from creating a
separate backend/data/ directory instead of using the root data/ folder.

Changes:
- Add getDataDir() to db-utils.ts as single source of truth
- Update all 8 source files that reference the data directory
- Add dotenv fallback to ../.env for local dev from backend/
- Add DATA_DIR documentation to .env.example
- Add 7 new tests for getDataDir and getDbPaths with DATA_DIR
- 493 tests pass, TypeScript clean

backend/src/test/database.test.ts

@@ -5,13 +5,14 @@ import { fileURLToPath } from "node:url";
 import { createClient } from "@libsql/client";
 import { drizzle } from "drizzle-orm/libsql";
 import { migrate } from "drizzle-orm/libsql/migrator";
-import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
 // Import utility functions from db-utils (no side effects, unlike client.ts which initializes the DB)
 import {
 	buildDbUrl,
 	ensureDataDirectory,
 	ensureDefaultUser,
+	getDataDir,
 	getDbPaths,
 	repairOrphanedDoseIds,
 	repairTrailingHyphenDoseIds,
@@ -144,8 +145,53 @@ describe("Database Client Utilities", () => {
 		});
 	});
 
+	describe("getDataDir", () => {
+		const originalDataDir = process.env.DATA_DIR;
+
+		afterEach(() => {
+			if (originalDataDir === undefined) {
+				delete process.env.DATA_DIR;
+			} else {
+				process.env.DATA_DIR = originalDataDir;
+			}
+		});
+
+		it("should use DATA_DIR env var when set", () => {
+			process.env.DATA_DIR = "/custom/data";
+			expect(getDataDir()).toBe("/custom/data");
+		});
+
+		it("should resolve relative DATA_DIR to absolute", () => {
+			process.env.DATA_DIR = "../data";
+			const result = getDataDir();
+			expect(result).not.toContain("..");
+			expect(result).toMatch(/\/data$/);
+		});
+
+		it("should fall back to cwd/data when DATA_DIR is not set", () => {
+			delete process.env.DATA_DIR;
+			expect(getDataDir("/app")).toBe("/app/data");
+		});
+
+		it("should use DATA_DIR even when cwd is provided", () => {
+			process.env.DATA_DIR = "/override/data";
+			expect(getDataDir("/app")).toBe("/override/data");
+		});
+	});
+
 	describe("getDbPaths", () => {
+		const originalDataDir = process.env.DATA_DIR;
+
+		afterEach(() => {
+			if (originalDataDir === undefined) {
+				delete process.env.DATA_DIR;
+			} else {
+				process.env.DATA_DIR = originalDataDir;
+			}
+		});
+
 		it("should return correct paths based on cwd", () => {
+			delete process.env.DATA_DIR;
 			const paths = getDbPaths("/app");
 			expect(paths.dataDir).toBe("/app/data");
 			expect(paths.dbPath).toBe("/app/data/medassist-ng.db");
@@ -153,10 +199,18 @@ describe("Database Client Utilities", () => {
 		});
 
 		it("should use process.cwd() by default", () => {
+			delete process.env.DATA_DIR;
 			const paths = getDbPaths();
 			expect(paths.dataDir).toContain("data");
 			expect(paths.dbPath).toContain("medassist-ng.db");
 		});
+
+		it("should respect DATA_DIR env var", () => {
+			process.env.DATA_DIR = "/custom/data";
+			const paths = getDbPaths("/app");
+			expect(paths.dataDir).toBe("/custom/data");
+			expect(paths.dbPath).toBe("/custom/data/medassist-ng.db");
+		});
 	});
 
 	describe("ensureDataDirectory", () => {