Rename Installation to Instance

Follows the portal: the noun is "instance" everywhere the app says it —
UI strings, CLI output, error details, docs and comments. The wire keys
(`instance_id`, `instance_token`) and the hub route this calls move with it.

An existing cloud.json is adopted rather than refused: without the key
alias the dataclass fails to parse, which the caller swallows and reads as
"never enrolled" instead of "reconnect".

`instance_key` on a node type becomes `target_key`. It means the outside
thing a node points at, which is a different sense of the word, and keeping
both would put two meanings of "instance" in one codebase.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015YrQnKV3bnQd4K342y8tKj

backend/fluksio/flow/nodes/base.py

@@ -179,7 +179,7 @@ class Node:
     idempotent: bool = True
 
     @classmethod
-    def instance_key(cls, params: dict[str, Any]) -> str | None:
+    def target_key(cls, params: dict[str, Any]) -> str | None:
         """Which outside thing these parameters point at, if any.
 
         Two nodes with the same key talk to the same broker topic, URL or

backend/fluksio/flow/nodes/http.py

@@ -189,7 +189,7 @@ class HttpNode(Node):
         )
 
     @classmethod
-    def instance_key(cls, params: dict[str, Any]) -> str | None:
+    def target_key(cls, params: dict[str, Any]) -> str | None:
         # ponytail: a webhook's stored url is the path before the flow name is
         # prefixed onto it, so two flows both receiving on "/tick" merge into
         # one neuron. Key on mode as well if that ever misleads.

backend/fluksio/flow/nodes/influx.py

@@ -18,7 +18,7 @@ def _influxdb() -> Any:
     """The client library, which is a `fluksio[server]` extra.
 
     Imported per use rather than at module level, because the node type is
-    registered at boot and an installation with no InfluxDB behind it should
+    registered at boot and an instance with no InfluxDB behind it should
     not have to carry the library to start.
     """
     try:
@@ -198,7 +198,7 @@ class InfluxDbNode(Node):
         queries: dict[str, dict[str, Any]] = {}
 
     @classmethod
-    def instance_key(cls, params: dict[str, Any]) -> str | None:
+    def target_key(cls, params: dict[str, Any]) -> str | None:
         """The bucket, which is the thing several flows share."""
         url, bucket = params.get("url"), params.get("bucket")
         return f"{url}/{bucket}" if url and bucket else None

backend/fluksio/flow/nodes/inject.py

@@ -1,6 +1,6 @@
 """Inject: the node that starts something, on a timer or on request.
 
-Node-RED's *inject* is the most placed trigger in a real installation — mostly
+Node-RED's *inject* is the most placed trigger in a real instance — mostly
 as a button someone presses, sometimes on an interval, occasionally once when
 everything comes up.
 """

backend/fluksio/flow/nodes/logic.py

@@ -2,7 +2,7 @@
 
 Anything here could be written as a `python` node — that is what the function
 node is for. These exist because the same handful of shapes account for most of
-a real installation, and a rule you fill in is easier to read on a canvas, and
+a real instance, and a rule you fill in is easier to read on a canvas, and
 to change, than five lines of code repeated eighty times.
 """
 
@@ -115,7 +115,7 @@ class ChangeNode(Node):
     """Reshape a value on its way past: scale, offset, map, or replace.
 
     Node-RED's *change*, which is the second most common node in a real
-    installation after the function.
+    instance after the function.
     """
 
     class Params(BaseModel):

backend/fluksio/flow/nodes/mqtt.py

@@ -24,7 +24,7 @@ def _aiomqtt() -> Any:
     """The client library, which is a `fluksio[server]` extra.
 
     Imported per use rather than at module level, because the node type is
-    registered at boot and an installation that talks to no broker should not
+    registered at boot and an instance that talks to no broker should not
     have to carry the library to start.
     """
     try:
@@ -218,7 +218,7 @@ class MqttNode(Node):
         json_key: str | dict[str, str] = ""
 
     @classmethod
-    def instance_key(cls, params: dict[str, Any]) -> str | None:
+    def target_key(cls, params: dict[str, Any]) -> str | None:
         """The broker and topic, which is one physical thing.
 
         A publisher and a subscriber on the same topic get the same key on