docs: surface -d/-n shorthand flags in README and USER_MANUAL

The 7f73f60 commit added -d for --debug and -n for --dry-run (on the
six mutation subcommands), but the docs still showed only the long
forms. Update three spots:

- README.md persistent-flags table: --debug row now reads `--debug, -d`
- README.md mutation paragraph: `--dry-run` → `--dry-run / -n`
- docs/USER_MANUAL.md persistent-flags table: same as README

Matches the existing convention used for `--category, -c` and
`--filter, -f`.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: jingle2008

README.md

@@ -124,7 +124,7 @@ toolkit --help                # all global flags
 | `--metadata-file` | `~/.config/toolkit/metadata.yaml` | Optional additional metadata file |
 | `--kubeconfig` | `~/.kube/config` | Path to kubeconfig file |
 | `--log-file` | `toolkit.log` | Path to log file |
-| `--debug` | `false` | Enable debug logging |
+| `--debug, -d` | `false` | Enable debug logging |
 | `--log-format` | `console` | Log format: `console`, `json`, or `slog` |
 | `--log-level` | | Minimum log level: `debug`, `info`, `warn`, `error` (empty uses `--debug` flag) |
 | `--mutation-env-override-allowed` | `false` | Allow MCP mutation tools to override the startup env per call (off by default for safety) |
@@ -179,7 +179,7 @@ toolkit config --validate         # run config.Validate(); exit non-zero on fail
 
 ### Cluster mutations
 
-Maintenance operations the TUI exposes via keyboard shortcuts are also available as scriptable subcommands. All mutations support `--dry-run` (preview the action) and `--yes` / `-y` (skip the interactive prompt). Each call writes a JSON line to the audit log.
+Maintenance operations the TUI exposes via keyboard shortcuts are also available as scriptable subcommands. All mutations support `--dry-run` / `-n` (preview the action) and `--yes` / `-y` (skip the interactive prompt). Each call writes a JSON line to the audit log.
 
 | Command | Effect |
 | ------- | ------ |

docs/USER_MANUAL.md

@@ -121,7 +121,7 @@ All flags can be set in the config file or passed directly on the command line.
 | `metadata-file` | `--metadata-file`  | `~/.config/toolkit/metadata.yaml`    | No       | Optional extra metadata file                 |
 | `config`        | `--config`         | `~/.config/toolkit/config.yaml`      | No       | Path to the config file itself               |
 | `log-file`      | `--log-file`       | `toolkit.log`                        | No       | Log output path                              |
-| `debug`         | `--debug`          | `false`                              | No       | Enable debug-level logging                   |
+| `debug`         | `-d / --debug`     | `false`                              | No       | Enable debug-level logging                   |
 | `log-format`    | `--log-format`     | `console`                            | No       | Log format: `console`, `json`, or `slog`     |
 | `log-level`     | `--log-level`      | `""`                                 | No       | Minimum log level: `debug` `info` `warn` `error` |