feat(cli): add --image-uri flag for self-hosted deployments (#8482)

Adds `--image-uri <uri>` to `langgraph deploy` so self-hosted LangSmith
customers can build, push, and deploy in one command without needing to
script the three steps manually.

When `--image-uri` is provided the CLI:
- Builds the image tagged to the provided URI (same Docker build path as
the local build flow)
- Pushes using whatever Docker credentials are already in the
environment (e.g. WIF, `aws ecr get-login-password`) — no auth handling
in the CLI
- PATCHes the deployment with `source_revision_config.image_uri` (no
`revision_source`, which the self-hosted control plane rejects for
`external_docker` deployments)

Also fixes two self-hosted-specific issues uncovered during testing:
- `LANGSMITH_ENDPOINT` is now used as a fallback when
`LANGGRAPH_HOST_URL` isn't set — the CLI strips the `/api/v1` path and
appends `/api-host` to reach the control plane
- The httpx client now builds full URLs via string concatenation rather
than relying on httpx base_url merging, which silently dropped the
`/api-host` path prefix when paths started with `/`
- The "Check status at" URL after a deploy now correctly points to the
self-hosted LangSmith UI instead of `smith.langchain.com`

**How did you verify your code works?**
Tested end-to-end against a self-hosted LangSmith instance using ECR as
the registry. `langgraph deploy --image-uri <ecr-uri>` successfully
built, pushed, and triggered a deployment revision. Confirmed the
existing SaaS flow (`langgraph deploy` without `--image-uri`) is
unaffected — the new flag is opt-in and the `LANGSMITH_ENDPOINT`
fallback only activates when `LANGGRAPH_HOST_URL` is unset and
`LANGSMITH_ENDPOINT` is present.

---------

Co-authored-by: Hari Dhanushkodi <hari-dhanushkodi@users.noreply.github.com>
Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>
Co-authored-by: Hugo Durand <hugo.durand@langchain.dev>

libs/cli/langgraph_cli/exec.py

@@ -1,12 +1,18 @@
 import asyncio
 import signal
 import sys
-from collections.abc import Callable
+from collections.abc import Callable, Coroutine
 from contextlib import contextmanager
-from typing import cast
+from typing import Any, Protocol, TypeVar, cast
 
 import click.exceptions
 
+_T = TypeVar("_T")
+
+
+class CommandRunner(Protocol):
+    def run(self, coro: Coroutine[Any, Any, _T]) -> _T: ...
+
 
 @contextmanager
 def Runner():