feat: add backup.retain_days config and local docker-compose for integration tests

- Add [backup] retain_days to config (default 1); --days becomes optional
- Add scripts/docker-compose.yml (azurite) for local integration testing
- Integration tests now use assets/local.toml and localhost endpoints
- Update .gitignore and CLAUDE.md accordingly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/config.toml

@@ -9,6 +9,9 @@ connection_string = ""
 # delay_ms = 200
 # scan_dir = "./scan"
 
+[backup]
+# retain_days = 1
+
 [delete]
 # batch_size = 100
 # delay_ms = 300

assets/local.toml

@@ -7,6 +7,9 @@ page_size = 500
 delay_ms = 200
 scan_dir = "./scan"
 
+[backup]
+retain_days = 1
+
 [delete]
 batch_size = 100
 delay_ms = 300

assets/s101.toml

@@ -7,6 +7,9 @@ page_size = 500
 delay_ms = 200
 scan_dir = "./scan"
 
+[backup]
+retain_days = 1
+
 [delete]
 batch_size = 100
 delay_ms = 300

assets/sandbox.toml

@@ -7,6 +7,9 @@ page_size = 500
 delay_ms = 200
 scan_dir = "./scan"
 
+[backup]
+retain_days = 1
+
 [delete]
 batch_size = 100
 delay_ms = 300