nodes: what porting the house needed from the vocabulary

Four small things, each with a device behind it.

An MQTT filter now routes what it subscribed to. `+` and `#` reached the
broker and were then looked up in an exact-match dict, so every message a
wildcard subscription received was dropped in silence.

`json_key` lifts a value out of the object a device wraps it in — Victron
publishes `{"value": 47}` on every path, which was otherwise a Python node
per port.

The trigger node learned `passthrough` and `wait_port`, because how long to
wait can be a value rather than a constant: a rollershutter takes 26 seconds
up and 28 down. A wait of zero sends nothing afterwards and still cancels
what the last message scheduled, which is how a stop is commanded once
instead of forever.

The HTTP sender takes fixed `query` parameters, so an API key is a secret
reference rather than a message on the canvas, and `send_inputs` off for a
request whose inputs are only a trigger.

Also: `delay` accepts fractional seconds, and `TZ` reaches the container, so
a cron expression means local time. Left unset it is UTC, as before.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/fluksio/flow/nodes/delay.py

@@ -100,8 +100,9 @@ class DelayNode(Node):
     class Params(BaseModel):
         model_config = ConfigDict(extra="allow")
 
-        delay: int = 0
-        interval: int = 0
+        # Seconds, fractional: a shutter's run-time is not a whole number.
+        delay: float = 0
+        interval: float = 0
         # Input port → output port; ports are paired in order when empty.
         mapping: dict[str, str] = {}
         cron: str | None = None