Refactor to modular app factory architecture

- Replace 6847-line monolithic server.py with 26-line entry point
- All routes now in app/routers/ using Jinja2 templates
- Add plan_node.html template for step details
- Add plan node route to runs router with cache_id lookup
- Backup old server as server_legacy.py

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

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

app/routers/runs.py

@@ -309,6 +309,110 @@ async def run_artifacts(
     )
 
 
+@router.get("/{run_id}/plan/node/{cache_id}", response_class=HTMLResponse)
+async def plan_node_detail(
+    run_id: str,
+    cache_id: str,
+    request: Request,
+    run_service: RunService = Depends(get_run_service),
+):
+    """HTMX partial: Get plan node detail by cache_id."""
+    from ..services.auth_service import AuthService
+    from artdag_common import render_fragment
+
+    auth_service = AuthService(get_redis_client())
+    ctx = auth_service.get_user_from_cookie(request)
+
+    if not ctx:
+        return HTMLResponse('<p class="text-red-400">Login required</p>', status_code=401)
+
+    run = await run_service.get_run(run_id)
+    if not run:
+        return HTMLResponse('<p class="text-red-400">Run not found</p>', status_code=404)
+
+    plan = await run_service.get_run_plan(run_id)
+    if not plan:
+        return HTMLResponse('<p class="text-gray-400">Plan not found</p>')
+
+    # Build lookups
+    steps_by_cache_id = {}
+    steps_by_step_id = {}
+    for s in plan.get("steps", []):
+        if s.get("cache_id"):
+            steps_by_cache_id[s["cache_id"]] = s
+        if s.get("step_id"):
+            steps_by_step_id[s["step_id"]] = s
+
+    step = steps_by_cache_id.get(cache_id)
+    if not step:
+        return HTMLResponse(f'<p class="text-gray-400">Step not found</p>')
+
+    cache_manager = get_cache_manager()
+
+    # Node colors
+    node_colors = {
+        "SOURCE": "#3b82f6", "EFFECT": "#22c55e", "OUTPUT": "#a855f7",
+        "ANALYSIS": "#f59e0b", "_LIST": "#6366f1", "default": "#6b7280"
+    }
+    node_color = node_colors.get(step.get("node_type", "EFFECT"), node_colors["default"])
+
+    # Check cache status
+    has_cached = cache_manager.has_content(cache_id) if cache_id else False
+
+    # Determine output media type
+    output_media_type = None
+    output_preview = False
+    if has_cached:
+        cache_path = cache_manager.get_content_path(cache_id)
+        if cache_path:
+            output_media_type = run_service.detect_media_type(cache_path)
+            output_preview = output_media_type in ('video', 'image', 'audio')
+
+    # Check for IPFS CID
+    ipfs_cid = None
+    if run.step_results:
+        res = run.step_results.get(step.get("step_id"))
+        if isinstance(res, dict) and res.get("cid"):
+            ipfs_cid = res["cid"]
+
+    # Build input previews
+    inputs = []
+    for inp_step_id in step.get("input_steps", []):
+        inp_step = steps_by_step_id.get(inp_step_id)
+        if inp_step:
+            inp_cache_id = inp_step.get("cache_id", "")
+            inp_has_cached = cache_manager.has_content(inp_cache_id) if inp_cache_id else False
+            inp_media_type = None
+            if inp_has_cached:
+                inp_path = cache_manager.get_content_path(inp_cache_id)
+                if inp_path:
+                    inp_media_type = run_service.detect_media_type(inp_path)
+
+            inputs.append({
+                "name": inp_step.get("name", inp_step_id[:12]),
+                "cache_id": inp_cache_id,
+                "media_type": inp_media_type,
+                "has_cached": inp_has_cached,
+            })
+
+    status = "cached" if (has_cached or ipfs_cid) else ("completed" if run.status == "completed" else "pending")
+
+    templates = get_templates(request)
+    return HTMLResponse(render_fragment(templates, "runs/plan_node.html",
+        step=step,
+        cache_id=cache_id,
+        node_color=node_color,
+        status=status,
+        has_cached=has_cached,
+        output_preview=output_preview,
+        output_media_type=output_media_type,
+        ipfs_cid=ipfs_cid,
+        ipfs_gateway="https://ipfs.io/ipfs",
+        inputs=inputs,
+        config=step.get("config", {}),
+    ))
+
+
 @router.delete("/{run_id}/ui", response_class=HTMLResponse)
 async def ui_discard_run(
     run_id: str,