Add a Python SDK: flows declared in your own repository

A data scientist keeps their code where it is and decorates it: `@node`
declares a function's ports beside the function, `Flow(name, nodes=[...])`
says which of them make a flow, and `use(fn, wire=..., **settings)` rebinds
one for a single flow. `fluksio sync` uploads the document plus a generated
import shim per node, so the store still holds a complete, runnable,
git-versioned definition while the code it imports stays theirs.

`fluksio login|run|runs` and `flow.submit().wait()` are the client half, over
the run endpoints that already existed. Runs record the user repository's
commit beside the store's, so "what code produced this number" is answerable
on the side that now holds the code.

- `fluksio/sdk/`: ports, decorators, the flow builder and its checks, the shim
  generator, an HTTP client and sync. Standard library only at import, so
  `from fluksio import node` in a training script pulls in no engine.
- `FlowDef.origin` marks a flow code-defined; `Run.origin_commit` carries the
  repository's commit; `POST /modules/refresh` retires the workers without an
  install, which every sync calls — a worker holds the imported package in
  memory, so an edit to it is invisible until the process goes.
- The canvas shows a generated body read-only and names the repository to edit
  instead; a body edited there stops the next sync rather than being discarded.
- The worker's reporter carries inert `Port`, `node`, `use` and `Flow`, since
  the shim imports a module whose first line declares them.
- `examples/myresearch` is the worked example, `make sync-example` uploads it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012ue1tkFWB1bcGy3aWhCKpU

backend/pyproject.toml

@@ -103,10 +103,13 @@ ignore = [
 "fluksio/__init__.py" = ["ARG001"]
 # It talks to whoever ran it; that is what a command line is.
 "fluksio/cli.py" = ["T201"]
+"fluksio/sdk/cli.py" = ["T201"]
 # Node functions take `params` whether or not they use it — that is the
 # contract the engine calls them with.
 "fluksio/flow/nodes.py" = ["ARG001", "ARG002"]
 "tests/flow/*" = ["ARG001"]
+# Node functions declared for a test take the ports they declare, used or not.
+"tests/sdk/*" = ["ARG001"]
 # Printing is what this one is about: node code is user code, and `print` is
 # how it says things.
 "tests/flow/test_logs.py" = ["ARG001", "T201"]