Initial artdag-common shared library

Shared components for L1 and L2 servers:
- Jinja2 template system with base template and components
- Middleware for auth and content negotiation
- Pydantic models for requests/responses
- Utility functions for pagination, media, formatting
- Constants for Tailwind/HTMX/Cytoscape CDNs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

artdag_common/utils/formatting.py

@@ -0,0 +1,165 @@
+"""
+Formatting utilities for display.
+"""
+
+from datetime import datetime
+from typing import Optional, Union
+
+
+def format_date(
+    value: Optional[Union[str, datetime]],
+    length: int = 10,
+    include_time: bool = False,
+) -> str:
+    """
+    Format a date/datetime for display.
+
+    Args:
+        value: Date string or datetime object
+        length: Length to truncate to (default 10 for YYYY-MM-DD)
+        include_time: Whether to include time portion
+
+    Returns:
+        Formatted date string
+    """
+    if value is None:
+        return ""
+
+    if isinstance(value, str):
+        # Parse ISO format string
+        try:
+            if "T" in value:
+                dt = datetime.fromisoformat(value.replace("Z", "+00:00"))
+            else:
+                return value[:length]
+        except ValueError:
+            return value[:length]
+    else:
+        dt = value
+
+    if include_time:
+        return dt.strftime("%Y-%m-%d %H:%M")
+    return dt.strftime("%Y-%m-%d")
+
+
+def format_size(size_bytes: Optional[int]) -> str:
+    """
+    Format file size in human-readable form.
+
+    Args:
+        size_bytes: Size in bytes
+
+    Returns:
+        Human-readable size string (e.g., "1.5 MB")
+    """
+    if size_bytes is None:
+        return "Unknown"
+    if size_bytes < 0:
+        return "Unknown"
+    if size_bytes == 0:
+        return "0 B"
+
+    units = ["B", "KB", "MB", "GB", "TB"]
+    unit_index = 0
+    size = float(size_bytes)
+
+    while size >= 1024 and unit_index < len(units) - 1:
+        size /= 1024
+        unit_index += 1
+
+    if unit_index == 0:
+        return f"{int(size)} {units[unit_index]}"
+    return f"{size:.1f} {units[unit_index]}"
+
+
+def truncate_hash(value: str, length: int = 16, suffix: str = "...") -> str:
+    """
+    Truncate a hash or long string with ellipsis.
+
+    Args:
+        value: String to truncate
+        length: Maximum length before truncation
+        suffix: Suffix to add when truncated
+
+    Returns:
+        Truncated string
+    """
+    if not value:
+        return ""
+    if len(value) <= length:
+        return value
+    return f"{value[:length]}{suffix}"
+
+
+def format_duration(seconds: Optional[float]) -> str:
+    """
+    Format duration in human-readable form.
+
+    Args:
+        seconds: Duration in seconds
+
+    Returns:
+        Human-readable duration string (e.g., "2m 30s")
+    """
+    if seconds is None or seconds < 0:
+        return "Unknown"
+
+    if seconds < 1:
+        return f"{int(seconds * 1000)}ms"
+
+    if seconds < 60:
+        return f"{seconds:.1f}s"
+
+    minutes = int(seconds // 60)
+    remaining_seconds = int(seconds % 60)
+
+    if minutes < 60:
+        if remaining_seconds:
+            return f"{minutes}m {remaining_seconds}s"
+        return f"{minutes}m"
+
+    hours = minutes // 60
+    remaining_minutes = minutes % 60
+
+    if remaining_minutes:
+        return f"{hours}h {remaining_minutes}m"
+    return f"{hours}h"
+
+
+def format_count(count: int) -> str:
+    """
+    Format a count with abbreviation for large numbers.
+
+    Args:
+        count: Number to format
+
+    Returns:
+        Formatted string (e.g., "1.2K", "3.5M")
+    """
+    if count < 1000:
+        return str(count)
+    if count < 1000000:
+        return f"{count / 1000:.1f}K"
+    if count < 1000000000:
+        return f"{count / 1000000:.1f}M"
+    return f"{count / 1000000000:.1f}B"
+
+
+def format_percentage(value: float, decimals: int = 1) -> str:
+    """
+    Format a percentage value.
+
+    Args:
+        value: Percentage value (0-100 or 0-1)
+        decimals: Number of decimal places
+
+    Returns:
+        Formatted percentage string
+    """
+    # Assume 0-1 if less than 1
+    if value <= 1:
+        value *= 100
+
+    if decimals == 0:
+        return f"{int(value)}%"
+    return f"{value:.{decimals}f}%"