Add flow settings, pulse emitting nodes, and simplify node state

- One dot per node now carries the whole story: primary while running, sage
  after a good run, red when anything is wrong, with the explanation on hover.
  The corner badge is gone, along with the second way of saying the same thing.
- A node that publishes something flashes a ring, so a running flow is legible
  without reading the edge values. Nodes that consume but publish nothing stay
  quiet, which is why the event carries an output count.
- Flow settings open in the same panel its nodes use, from a pencil in the
  dock: the title, the name, and deleting the flow. NodePanel and FlowPanel
  share the panel chrome rather than each drawing their own.
- Renaming is a server operation, because a flow's name is the namespace of its
  messages: the directory moves and every other flow reading `old.message` is
  repointed, instead of being left pointing at a flow that no longer exists.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WzrvW7rjQbynnhF6pxh6i

backend/app/api/routes/flows.py

@@ -21,6 +21,7 @@ from app.flow.events import event_bus
 from app.flow.messages import qualify
 from app.flow.pipeline import ValidationIssue
 from app.flow.schemas import (
+    NAME_PATTERN,
     FlowDef,
     FlowsPublic,
     FlowStatePublic,
@@ -30,7 +31,7 @@ from app.flow.schemas import (
     NodeStatusPublic,
     NodeTypeInfo,
 )
-from app.flow.store import FlowNotFound
+from app.flow.store import FlowExists, FlowNotFound
 from app.models import Message
 
 router = APIRouter(
@@ -53,6 +54,10 @@ class ValidationResult(BaseModel):
     issues: list[ValidationIssue] = []
 
 
+class RenameRequest(BaseModel):
+    new_name: str
+
+
 class RunRequest(BaseModel):
     inputs: dict[str, Any] = {}
 
@@ -154,6 +159,33 @@ async def delete_flow(name: str, controller: FlowControllerDep) -> Any:
     return Message(message=f"Deleted flow '{name}'")
 
 
+@router.post("/{name}/rename", response_model=FlowDetail)
+async def rename_flow(
+    name: str,
+    body: RenameRequest,
+    controller: FlowControllerDep,
+) -> Any:
+    """Rename a flow, along with every reference to its messages."""
+    if not NAME_PATTERN.match(body.new_name):
+        raise HTTPException(
+            status_code=400,
+            detail=(
+                "Use lowercase letters, digits and underscores, starting with a letter"
+            ),
+        )
+    try:
+        renamed = await run_in_threadpool(
+            controller.store.rename_flow, name, body.new_name
+        )
+    except FlowNotFound:
+        raise HTTPException(status_code=404, detail=f"No flow named '{name}'")
+    except FlowExists as exc:
+        raise HTTPException(status_code=409, detail=str(exc))
+
+    await controller.reload()
+    return _detail(controller, renamed)
+
+
 # -----------------------------------------------------------------------------
 # Node source
 # -----------------------------------------------------------------------------