feat: remove unused image retrieval endpoint and add human-readable time formatting filters

Co-authored-by: Copilot <copilot@github.com>

frontend/app/main.py

@@ -1,5 +1,6 @@
 """Flask frontend application."""
 import functools
+from datetime import datetime, timezone
 
 import httpx
 from flask import (
@@ -24,6 +25,42 @@ app.config.from_object(Config)
 # Helpers
 # ---------------------------------------------------------------------------
 
+@app.template_filter("fromisoformat")
+def from_iso_format(s: str) -> datetime:
+    """Convert ISO 8601 string to datetime object."""
+    return datetime.fromisoformat(s)
+
+
+@app.template_filter("humantime")
+def human_time(dt: datetime) -> str:
+    """Format a datetime object into a human-readable relative time."""
+    now = datetime.now(timezone.utc)
+    # Ensure dt is aware for comparison
+    if dt.tzinfo is None:
+        dt = dt.replace(tzinfo=timezone.utc)
+
+    diff = now - dt
+    seconds = diff.total_seconds()
+
+    if seconds < 60:
+        return "just now"
+    elif seconds < 3600:
+        minutes = int(seconds / 60)
+        return f"{minutes} minute{'s' if minutes > 1 else ''} ago"
+    elif seconds < 86400:
+        hours = int(seconds / 3600)
+        return f"{hours} hour{'s' if hours > 1 else ''} ago"
+    elif seconds < 2592000:
+        days = int(seconds / 86400)
+        return f"{days} day{'s' if days > 1 else ''} ago"
+    elif seconds < 31536000:
+        months = int(seconds / 2592000)
+        return f"{months} month{'s' if months > 1 else ''} ago"
+    else:
+        years = int(seconds / 31536000)
+        return f"{years} year{'s' if years > 1 else ''} ago"
+
+
 def _backend(path: str) -> str:
     return f"{app.config['BACKEND_URL']}{path}"