feat: mysql-bkup v2 on bkupkit

MysQL backup and restore built on the shared bkupkit core:
streaming end to end, with no dump held in memory or written to
local disk.

docs/how-tos/encrypt-backup.md

@@ -42,7 +42,7 @@ services:
       - DB_PORT=3306
       - DB_HOST=mysql
       - DB_NAME=database
-      - DB_USERNAME=username
+      - DB_USER=username
       - DB_PASSWORD=password
       ## Required to encrypt backup
       - GPG_PASSPHRASE=my-secure-passphrase
@@ -58,7 +58,7 @@ networks:
 
 ## Using GPG Public Key
 
-To encrypt backups using a GPG public key, set the `GPG_PUBLIC_KEY` environment variable to the path of your public key file. Backups encrypted with a public key require manual decryption before restoration.
+To encrypt backups using a GPG public key, set the `GPG_PUBLIC_KEY` environment variable to the path of your public key file. To restore such backups, set `GPG_PRIVATE_KEY` (a file path or the inline armored key; `/config/gnupg/private_key.asc` is picked up automatically) and, if the key is protected, `GPG_PRIVATE_KEY_PASSPHRASE` (defaults to `GPG_PASSPHRASE`).
 
 ### Example Configuration
 
@@ -78,7 +78,7 @@ services:
       - DB_PORT=3306
       - DB_HOST=mysql
       - DB_NAME=database
-      - DB_USERNAME=username
+      - DB_USER=username
       - DB_PASSWORD=password
       ## Required to encrypt backup
       - GPG_PUBLIC_KEY=/config/public_key.asc
@@ -116,5 +116,21 @@ gpg --output database_20240730_044201.sql.gz \
 ## Key Notes
 
 - **Automatic Restoration**: Backups encrypted with a GPG passphrase can be restored directly without manual decryption.
-- **Manual Decryption**: Backups encrypted with a GPG public key require manual decryption using the corresponding private key.
+- **Private key restore**: Backups encrypted with a GPG public key restore directly when `GPG_PRIVATE_KEY` is set; manual decryption also works.
+- **Fail closed**: if `GPG_PUBLIC_KEY` (or any configured key) cannot be read, the backup fails instead of being stored unencrypted.
 - **Security**: Always keep your GPG passphrase and private key secure. Use Kubernetes Secrets or other secure methods to manage sensitive data.
+
+---
+
+## Using age
+
+[age](https://age-encryption.org) is a modern alternative to GPG. Set `AGE_RECIPIENTS` (one or more `age1...` or `ssh-ed25519 ...` public keys, comma or newline separated, or `AGE_RECIPIENTS_FILE`) and backups are saved as `.sql.gz.age`. Restore with the matching identity in `AGE_IDENTITY` (`AGE-SECRET-KEY-...`) or `AGE_IDENTITY_FILE` (default `/config/age/identity.txt`).
+
+```yaml
+    environment:
+      - AGE_RECIPIENTS=age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
+      # restore:
+      # - AGE_IDENTITY_FILE=/run/secrets/age_identity
+```
+
+`AGE_PASSPHRASE` encrypts with a passphrase instead (it needs about 256 MiB of memory for the key derivation). `ENCRYPTION=auto|none|gpg|age` chooses explicitly; with `auto` (default) GPG wins when both GPG and age keys are set. Decrypt by hand with `age -d -i key.txt file.sql.gz.age | gunzip`.