feat: pass alarm style through crontab manager and GraphQL API

- crontab_manager.get_alarms now parses --style from the cron command
  (defaults to 'blink' for legacy entries without --style)
- GraphQL Alarm type gains a 'style' field
- setAlarm accepts a 'style' arg (default 'simple') and validates it
  against the styles registry; unknown styles raise a GraphQL error
- _default_command embeds --style <name> into the cron command
- startRinging accepts 'style' (default 'simple') and passes --style to
  the spawned wecker.py

The crontab remains the single source of truth; the style simply rides
in the cron command alongside --music-file.

api/crontab_manager.py

@@ -1,6 +1,9 @@
+import shlex
 import uuid
 from crontab import CronTab, CronSlices
 
+from styles import LEGACY_STYLE
+
 
 class CrontabManager:
     COMMENT_PREFIX = "wecker-alarm:"
@@ -28,6 +31,7 @@ class CrontabManager:
                         "cron_expression": str(job.slices),
                         "command": job.command,
                         "is_enabled": job.is_enabled(),
+                        "style": _parse_style(job.command),
                     }
                 )
         return alarms
@@ -64,3 +68,21 @@ class CrontabManager:
         comment = f"{self.COMMENT_PREFIX}{alarm_id}"
         cron.remove_all(comment=comment)
         cron.write()
+
+
+def _parse_style(command: str) -> str:
+    """Extract the --style value from a cron command.
+
+    Returns LEGACY_STYLE ('blink') for entries that predate --style, so an
+    upgrade never silently changes an existing alarm's behaviour.
+    """
+    try:
+        tokens = shlex.split(command)
+    except ValueError:
+        return LEGACY_STYLE
+    for i, tok in enumerate(tokens):
+        if tok == "--style" and i + 1 < len(tokens):
+            return tokens[i + 1]
+        if tok.startswith("--style="):
+            return tok.split("=", 1)[1]
+    return LEGACY_STYLE