A profile may load weights of its own

The catalog had one source a model, so an embedding model served by vLLM
from its repository on a card and by llama.cpp from a GGUF on CPUs had its
entry swapped by hand halfway through the metallurgy import. A profile's
source is what its engine loads and placement looks for; the model's is
the default, and what updates and canaries move. ctl model add checks
every source, the GGUF check reads each llama.cpp profile's, and ctl
weights collects none a profile loads. An empty source leaves a profile's
fingerprint as it was, so running replicas do not read as stale.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/reference.md

@@ -220,6 +220,7 @@ rather than repeated.
 | `engine` | `string` | [Profile](#profile) |
 | `engine_version` | `string` | [Profile](#profile) |
 | `gpu_class` | `string` | [Profile](#profile) |
+| `source` | `string` | [Profile](#profile) |
 | `tp` | `int` | [Profile](#profile) |
 | `pp` | `int` | [Profile](#profile) |
 | `gpus_per_node` | `int` | [Profile](#profile) |
@@ -1925,6 +1926,16 @@ version starts with it: "0.11" takes vLLM 0.11.0 and 0.11.1, not
 
 `string`
 
+### `source`
+
+`string`
+
+Source is the weights this profile loads, when not the model's: an
+embedding model served by vLLM from its repository on a card and by
+llama.cpp from a GGUF on CPUs is one model with two sources. Empty
+loads the model's. Updates and canaries move the model's source; a
+profile with its own keeps it.
+
 ### `tp`
 
 `int`