fix(api): chemins de bibliothèques — validation dédiée, alias et unicité

Validation des chemins externalisée (library-path) avec codes d'erreur
explicites, support d'alias LIBRARY_PATH_ALIASES pour traduire un chemin
hôte vers le montage conteneur, rejet des doublons de chemin entre
bibliothèques, documentation README/.env.example et docker-compose
paramétrable via READABOOK_LIBRARY_HOST_PATH.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/api/src/libraries/library-path.test.ts

@@ -0,0 +1,49 @@
+import { closeSync, existsSync, mkdtempSync, openSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join, resolve } from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { LibraryPathValidationError, resolveLibraryPath } from "./library-path.js";
+
+const tempDirs: string[] = [];
+const realBooksPath = "/home/anthony/Documents/Projects/ReadaBook/Books";
+
+afterEach(() => {
+  for (const dir of tempDirs.splice(0)) {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});
+
+describe("library path resolution", () => {
+  it("resolves a readable directory", () => {
+    const dir = mkdtempSync(join(tmpdir(), "readabook-library-"));
+    tempDirs.push(dir);
+
+    expect(resolveLibraryPath(dir)).toBe(resolve(dir));
+  });
+
+  it("maps a host path alias to the mounted container path", () => {
+    const hostRoot = "/host/project/Books";
+    const mountedRoot = mkdtempSync(join(tmpdir(), "readabook-mounted-books-"));
+    tempDirs.push(mountedRoot);
+
+    expect(resolveLibraryPath(hostRoot, [{ from: hostRoot, to: mountedRoot }])).toBe(resolve(mountedRoot));
+  });
+
+  it("rejects regular files with a stable code", () => {
+    const dir = mkdtempSync(join(tmpdir(), "readabook-library-"));
+    tempDirs.push(dir);
+    const file = join(dir, "book.epub");
+    closeSync(openSync(file, "w"));
+
+    expect(() => resolveLibraryPath(file)).toThrowError(LibraryPathValidationError);
+    try {
+      resolveLibraryPath(file);
+    } catch (error) {
+      expect(error).toMatchObject({ code: "LIBRARY_PATH_NOT_DIRECTORY" });
+    }
+  });
+
+  it.runIf(existsSync(realBooksPath))("accepts the real Books corpus path used by QA", () => {
+    expect(resolveLibraryPath(realBooksPath)).toBe(resolve(realBooksPath));
+  });
+});