refactor: extract magic numbers as named constants in _output and _frontmatter

Replace hardcoded `60` in format_duration with _SECONDS_PER_MINUTE and
_MINUTES_PER_HOUR constants. Extract UTF-8 BOM character literal as
_UTF8_BOM constant and use str.removeprefix for clearer intent.

Co-authored-by: Ralphify <noreply@ralphify.co>

Author: 2 people

src/ralphify/_frontmatter.py

@@ -42,6 +42,9 @@
 # Human-readable description of allowed name characters, paired with CMD_NAME_RE.
 VALID_NAME_CHARS_MSG = "Names may only contain letters, digits, hyphens, and underscores."
 
+# UTF-8 BOM character — files saved on Windows may start with this.
+_UTF8_BOM = "\ufeff"
+
 # Pre-compiled pattern to strip HTML comments from body text.
 _HTML_COMMENT_RE = re.compile(r"<!--.*?-->", re.DOTALL)
 
@@ -77,8 +80,8 @@ def parse_frontmatter(text: str) -> tuple[dict[str, Any], str]:
 
     Returns ``(frontmatter_dict, body_text)``.
     """
-    if text.startswith("\ufeff"):
-        text = text[1:]
+    if text.startswith(_UTF8_BOM):
+        text = text.removeprefix(_UTF8_BOM)
     fm_raw, body = _extract_frontmatter_block(text)
     if fm_raw:
         try:

src/ralphify/_output.py

@@ -64,21 +64,25 @@ def collect_output(
     return "".join(parts)
 
 
+_SECONDS_PER_MINUTE = 60
+_MINUTES_PER_HOUR = 60
+
+
 def format_duration(seconds: float) -> str:
     """Format *seconds* as a compact human-readable duration string.
 
     Returns ``"12.3s"`` for sub-minute, ``"2m 30s"`` for sub-hour,
     and ``"1h 15m"`` for longer durations.  Used in CLI output and
     event data for iteration timing.
     """
-    if round(seconds, 1) < 60:
+    if round(seconds, 1) < _SECONDS_PER_MINUTE:
         return f"{seconds:.1f}s"
     # Use rounded total to avoid edge cases like 59.95 → "0m 60s"
     total = round(seconds)
-    minutes = total // 60
-    secs = total % 60
-    if minutes < 60:
+    minutes = total // _SECONDS_PER_MINUTE
+    secs = total % _SECONDS_PER_MINUTE
+    if minutes < _MINUTES_PER_HOUR:
         return f"{minutes}m {secs}s"
-    hours = minutes // 60
-    mins = minutes % 60
+    hours = minutes // _MINUTES_PER_HOUR
+    mins = minutes % _MINUTES_PER_HOUR
     return f"{hours}h {mins}m"