Move tests out of src/ into a top-level tests/ directory

src/ now contains only source code; tests live alongside it under
tests/. Bun's test runner discovers '**/*.test.ts' so no test-runner
config change is needed.

Changes:
  - tests/config.test.ts        (was src/config.test.ts)
  - tests/configFile.test.ts    (was src/configFile.test.ts)
  - Imports updated: ./config.ts -> ../src/config.ts (likewise for
    configFile.ts and errors.ts).
  - tsconfig.json include adds 'tests/**/*.ts' so tsc type-checks
    the test files too.

All 25 tests still pass; tsc clean.

tests/configFile.test.ts

@@ -0,0 +1,120 @@
+/**
+ * configFile.test.ts
+ * ------------------
+ * Unit tests for the JSON config-file loader.
+ * Run via `bun test` (or `bun run test`).
+ */
+
+import { afterAll, beforeAll, describe, expect, test } from "bun:test";
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { loadConfigFile } from "../src/configFile.ts";
+import { CliError } from "../src/errors.ts";
+
+let TMP: string;
+
+beforeAll(() => {
+    TMP = mkdtempSync(join(tmpdir(), "move-cfg-test-"));
+});
+
+afterAll(() => {
+    rmSync(TMP, { recursive: true, force: true });
+});
+
+function writeFixture(name: string, body: string): string {
+    const p = join(TMP, name);
+    writeFileSync(p, body);
+    return p;
+}
+
+describe("loadConfigFile (explicit path)", () => {
+    test("returns parsed overrides for a valid file", () => {
+        const path = writeFixture(
+            "valid.json",
+            JSON.stringify({ moveInterval: 60, verbose: true }),
+        );
+        const result = loadConfigFile(path);
+        expect(result).not.toBeNull();
+        // The bang is justified by the not-null assertion above.
+        expect(result!.moveInterval).toBe(60);
+        expect(result!.verbose).toBe(true);
+        // Fields not in the file are undefined.
+        expect(result!.checkInterval).toBeUndefined();
+        expect(result!.stepDelay).toBeUndefined();
+        expect(result!.stepCount).toBeUndefined();
+    });
+
+    test("returns all-undefined overrides for an empty object", () => {
+        const path = writeFixture("empty.json", "{}");
+        const result = loadConfigFile(path);
+        expect(result).not.toBeNull();
+        expect(result!.moveInterval).toBeUndefined();
+        expect(result!.verbose).toBeUndefined();
+    });
+
+    test("throws CliError when explicit path does not exist", () => {
+        expect(() => loadConfigFile(join(TMP, "missing.json"))).toThrow(CliError);
+    });
+
+    test("throws on malformed JSON, mentioning the file path", () => {
+        const path = writeFixture("bad-json.json", "this is not json");
+        expect(() => loadConfigFile(path)).toThrow(/is not valid JSON/);
+        expect(() => loadConfigFile(path)).toThrow(new RegExp(path.replace(/[.]/g, "\\.")));
+    });
+
+    test("throws when root is not an object (e.g. array)", () => {
+        const path = writeFixture("array.json", "[1, 2, 3]");
+        expect(() => loadConfigFile(path)).toThrow(/JSON object at the root/);
+    });
+
+    test("throws when root is not an object (e.g. string)", () => {
+        const path = writeFixture("string.json", "\"hello\"");
+        expect(() => loadConfigFile(path)).toThrow(/JSON object at the root/);
+    });
+
+    test("throws on an unknown key, naming the typo and the allowed set", () => {
+        const path = writeFixture("typo.json", JSON.stringify({ movInterval: 60 }));
+        expect(() => loadConfigFile(path)).toThrow(/unknown key 'movInterval'/);
+        expect(() => loadConfigFile(path)).toThrow(/moveInterval/);
+    });
+
+    test("throws on non-positive numeric values", () => {
+        const negative = writeFixture("neg.json", JSON.stringify({ stepCount: -1 }));
+        expect(() => loadConfigFile(negative)).toThrow(/'stepCount'.*positive number/);
+
+        const zero = writeFixture("zero.json", JSON.stringify({ stepDelay: 0 }));
+        expect(() => loadConfigFile(zero)).toThrow(/'stepDelay'.*positive number/);
+    });
+
+    test("throws when a numeric field has the wrong type", () => {
+        const path = writeFixture("type.json", JSON.stringify({ moveInterval: "60" }));
+        expect(() => loadConfigFile(path)).toThrow(/'moveInterval'.*positive number/);
+    });
+
+    test("throws when verbose is the wrong type", () => {
+        const path = writeFixture("verbose.json", JSON.stringify({ verbose: "yes" }));
+        expect(() => loadConfigFile(path)).toThrow(/'verbose'.*boolean/);
+    });
+});
+
+describe("loadConfigFile (default path)", () => {
+    let savedXdg: string | undefined;
+
+    beforeAll(() => {
+        savedXdg = process.env.XDG_CONFIG_HOME;
+        // Point the default path under the test tmpdir so a missing file is
+        // guaranteed (we never create $TMP/move/config.json).
+        process.env.XDG_CONFIG_HOME = TMP;
+    });
+
+    afterAll(() => {
+        if (savedXdg === undefined) delete process.env.XDG_CONFIG_HOME;
+        else process.env.XDG_CONFIG_HOME = savedXdg;
+    });
+
+    test("returns null when no file exists at the default path", () => {
+        expect(loadConfigFile(undefined)).toBeNull();
+    });
+});