fix(backup): restore from Docker, fail-fast on shadowed /app, bundle encryption key (#1193) (#1197)

* fix(backup): restore uploads through symlinked dir and bundle encryption key (#1193)

Restoring a backup inside Docker threw ERR_FS_CP_DIR_TO_NON_DIR because
/app/server/uploads is a symlink to the mounted /app/uploads volume and
cpSync (dereference:false) refuses to overwrite the symlink node with a
directory. The DB was swapped before this failing copy, so users saw
restored data but missing upload files (trip covers). Resolve the symlink
with realpathSync before copying so the merge targets the real directory;
no-op on a plain dir, so non-Docker behavior is unchanged.

Also bundle the at-rest encryption key (data/.encryption_key) into the
backup so a restore onto a different install can decrypt stored secrets
(API keys, MFA, SMTP/OIDC). Skipped when ENCRYPTION_KEY is provided via
env (the file is not the source of truth then). On restore the key is
swapped back if the archive carries one; a restart is required for the
in-memory key to take effect.

* fix(docker): fail fast when a volume shadows /app (#1193)

Mounting an old volume at /app hides the image's node_modules and dist,
so startup crashed with a cryptic "Cannot find module
'tsconfig-paths/register'". Add a CMD preflight that detects the missing
app files and exits with actionable guidance. Document in the README that
only /app/data and /app/uploads should be mounted, never /app.

* fix: ssrf test

README.md

@@ -311,6 +311,9 @@ docker run -d --name trek -p 3000:3000 -v ./data:/app/data -v ./uploads:/app/upl
 
 Your data stays in the mounted `data` and `uploads` volumes — updates never touch it.
 
+> [!IMPORTANT]
+> Mount **only** the data and uploads directories — `-v ./data:/app/data -v ./uploads:/app/uploads`. **Never mount a volume at `/app`.** Doing so hides the application code shipped in the image and the container fails to start with `Cannot find module 'tsconfig-paths/register'`. If you previously mounted `/app`, switch to the two mounts above; your data in `data/` and `uploads/` is preserved.
+
 <h3>Rotating the Encryption Key</h3>
 
 If you need to rotate `ENCRYPTION_KEY` (e.g. upgrading from a version that derived encryption from `JWT_SECRET`):