feat: Add notification email compression feature

Add intelligent notification email detection and compression:
- Detect notification emails from GitLab, GitHub, Jira, Confluence, Datadog, Renovate
- Extract structured summaries from notification emails
- Compress notifications into terminal-friendly markdown format
- Add configuration options for notification compression mode

Features:
- Rule-based detection using sender domains and subject patterns
- Type-specific extractors for each notification platform
- Configurable compression modes (summary, detailed, off)
- Integrated with ContentContainer for seamless display

Files added:
- src/mail/notification_detector.py: Notification type detection
- src/mail/notification_compressor.py: Content compression

Modified:
- src/mail/config.py: Add notification_compression_mode config
- src/mail/widgets/ContentContainer.py: Integrate compressor
- src/mail/app.py: Pass envelope data to display_content
- PROJECT_PLAN.md: Document new feature

src/mail/notification_compressor.py

@@ -0,0 +1,221 @@
+"""Notification email compressor for terminal-friendly display."""
+
+from typing import Dict, Any, Optional
+from textual.widgets import Markdown
+
+from .notification_detector import (
+    is_notification_email,
+    classify_notification,
+    extract_notification_summary,
+    NotificationType,
+)
+
+
+class NotificationCompressor:
+    """Compress notification emails into terminal-friendly summaries."""
+
+    def __init__(self, mode: str = "summary"):
+        """Initialize compressor.
+
+        Args:
+            mode: Compression mode - "summary", "detailed", or "off"
+        """
+        self.mode = mode
+
+    def should_compress(self, envelope: Dict[str, Any]) -> bool:
+        """Check if email should be compressed.
+
+        Args:
+            envelope: Email envelope metadata
+
+        Returns:
+            True if email should be compressed
+        """
+        if self.mode == "off":
+            return False
+
+        return is_notification_email(envelope)
+
+    def compress(
+        self, content: str, envelope: Dict[str, Any]
+    ) -> tuple[str, Optional[NotificationType]]:
+        """Compress notification email content.
+
+        Args:
+            content: Raw email content
+            envelope: Email envelope metadata
+
+        Returns:
+            Tuple of (compressed content, notification_type)
+        """
+
+        if not self.should_compress(envelope):
+            return content, None
+
+        # Classify notification type
+        notif_type = classify_notification(envelope, content)
+
+        # Extract summary
+        summary = extract_notification_summary(content, notif_type)
+
+        # Format as markdown
+        compressed = self._format_as_markdown(summary, envelope, notif_type)
+
+        return compressed, notif_type
+
+    def _format_as_markdown(
+        self,
+        summary: Dict[str, Any],
+        envelope: Dict[str, Any],
+        notif_type: Optional[NotificationType],
+    ) -> str:
+        """Format summary as markdown for terminal display.
+
+        Args:
+            summary: Extracted summary data
+            envelope: Email envelope metadata
+            notif_type: Classified notification type
+
+        Returns:
+            Markdown-formatted compressed email
+        """
+
+        from_addr = envelope.get("from", {}).get("name") or envelope.get(
+            "from", {}
+        ).get("addr", "")
+        subject = envelope.get("subject", "")
+
+        # Get icon
+        icon = notif_type.icon if notif_type else "\uf0f3"
+
+        # Build markdown
+        lines = []
+
+        # Header with icon
+        if notif_type:
+            lines.append(f"## {icon} {notif_type.name.title()} Notification")
+        else:
+            lines.append(f"## {icon} Notification")
+
+        lines.append("")
+
+        # Title/subject
+        if summary.get("title"):
+            lines.append(f"**{summary['title']}**")
+        else:
+            lines.append(f"**{subject}**")
+        lines.append("")
+
+        # Metadata section
+        if summary.get("metadata"):
+            lines.append("### Details")
+            for key, value in summary["metadata"].items():
+                # Format key nicely
+                key_formatted = key.replace("_", " ").title()
+                lines.append(f"- **{key_formatted}**: {value}")
+            lines.append("")
+
+        # Action items
+        if summary.get("action_items"):
+            lines.append("### Actions")
+            for i, action in enumerate(summary["action_items"], 1):
+                lines.append(f"{i}. {action}")
+            lines.append("")
+
+        # Add footer
+        lines.append("---")
+        lines.append("")
+        lines.append(f"*From: {from_addr}*")
+        lines.append(
+            "*This is a compressed notification view. Press `m` to toggle full view.*"
+        )
+
+        return "\n".join(lines)
+
+
+class DetailedCompressor(NotificationCompressor):
+    """Compressor that includes more detail in summaries."""
+
+    def _format_as_markdown(
+        self,
+        summary: Dict[str, Any],
+        envelope: Dict[str, Any],
+        notif_type: Optional[NotificationType],
+    ) -> str:
+        """Format summary with more detail."""
+
+        from_addr = envelope.get("from", {}).get("name") or envelope.get(
+            "from", {}
+        ).get("addr", "")
+        subject = envelope.get("subject", "")
+        date = envelope.get("date", "")
+
+        icon = notif_type.icon if notif_type else "\uf0f3"
+
+        lines = []
+
+        # Header
+        lines.append(
+            f"## {icon} {notif_type.name.title()} Notification"
+            if notif_type
+            else f"## {icon} Notification"
+        )
+        lines.append("")
+
+        # Subject and from
+        lines.append(f"**Subject:** {subject}")
+        lines.append(f"**From:** {from_addr}")
+        lines.append(f"**Date:** {date}")
+        lines.append("")
+
+        # Summary title
+        if summary.get("title"):
+            lines.append(f"### {summary['title']}")
+            lines.append("")
+
+        # Metadata table
+        if summary.get("metadata"):
+            lines.append("| Property | Value |")
+            lines.append("|----------|-------|")
+            for key, value in summary["metadata"].items():
+                key_formatted = key.replace("_", " ").title()
+                lines.append(f"| {key_formatted} | {value} |")
+            lines.append("")
+
+        # Action items
+        if summary.get("action_items"):
+            lines.append("### Action Items")
+            for i, action in enumerate(summary["action_items"], 1):
+                lines.append(f"- [ ] {action}")
+            lines.append("")
+
+        # Key links
+        if summary.get("key_links"):
+            lines.append("### Important Links")
+            for link in summary["key_links"]:
+                lines.append(f"- [{link.get('text', 'Link')}]({link.get('url', '#')})")
+            lines.append("")
+
+        # Footer
+        lines.append("---")
+        lines.append(
+            "*This is a compressed notification view. Press `m` to toggle full view.*"
+        )
+
+        return "\n".join(lines)
+
+
+def create_compressor(mode: str) -> NotificationCompressor:
+    """Factory function to create appropriate compressor.
+
+    Args:
+        mode: Compression mode - "summary", "detailed", or "off"
+
+    Returns:
+        NotificationCompressor instance
+    """
+
+    if mode == "detailed":
+        return DetailedCompressor(mode=mode)
+    else:
+        return NotificationCompressor(mode=mode)