fix: resolve milestone listing GraphQL filter issues

- Replace server-side filtering with client-side filtering for project milestones
- Add proper data structure handling in milestone listing command
- Fix GraphQL schema incompatibility with ProjectMilestoneFilter

This resolves issues where milestone listing by project would fail due to
Linear's GraphQL API not supporting direct project filtering for milestones.
The fix ensures reliable milestone listing by fetching all milestones and
filtering them client-side based on project ID.

Author: AdiKsOnDev

src/linear_cli/cli/commands/project.py

@@ -349,16 +349,29 @@ async def fetch_milestones() -> dict[str, Any]:
             print_error(f"Project not found: {project_id}")
             return {}
 
-        result = await client.get_milestones(
-            project_id=project_data["id"],
-            limit=limit
-        )
-        return dict(result) if isinstance(result, dict) else {}
+        # Get all milestones and filter client-side
+        # WHY: Linear's GraphQL schema doesn't support project filtering for milestones
+        # so we fetch all milestones and filter by project ID on the client side
+        result = await client.get_milestones(limit=limit)
+        if isinstance(result, dict) and "nodes" in result:
+            # Filter milestones by project ID
+            project_milestones = []
+            for milestone in result["nodes"]:
+                if milestone.get("project", {}).get("id") == project_data["id"]:
+                    project_milestones.append(milestone)
+            
+            return {
+                "nodes": project_milestones,
+                "pageInfo": result.get("pageInfo", {})
+            }
+        
+        return {}
 
     try:
         milestones_data = asyncio.run(fetch_milestones())
-        if milestones_data:
-            formatter.format_milestones(milestones_data)
+        if milestones_data and milestones_data.get("nodes"):
+            # Pass the nodes list to the formatter
+            formatter.format_milestones(milestones_data["nodes"])
     except Exception as e:
         print_error(f"Failed to list project milestones: {e}")
         raise click.Abort() from e
@@ -388,15 +401,14 @@ def show_milestone(ctx: click.Context, project_id: str, milestone_id: str) -> No
     )
 
     async def fetch_milestone() -> dict[str, Any] | None:
-        # First try direct lookup
-        milestone_data = await client.get_milestone(milestone_id)
-        if not milestone_data:
-            # Try resolving by name within project context
-            resolved_id = await client.resolve_milestone_id(milestone_id, project_id)
-            if resolved_id:
-                milestone_data = await client.get_milestone(resolved_id)
+        # WHY: Always resolve milestone ID first since user can provide either ID or name
+        # Direct lookup only works with actual milestone IDs, not names
+        resolved_id = await client.resolve_milestone_id(milestone_id, project_id)
+        if resolved_id:
+            milestone_data = await client.get_milestone(resolved_id)
+            return dict(milestone_data) if milestone_data else None
 
-        return dict(milestone_data) if milestone_data else None
+        return None
 
     try:
         milestone_data = asyncio.run(fetch_milestone())