feat: add stdout output for tesseract build (#87)

#### Relevant issue or PR
n/a

#### Description of changes
`tesseract build` now prints a JSON representation of the tags of the
built image to stdout. This allows scripts to discover the correct
Docker image to use for further processing (in cases where the Tesseract
name is unknown).

#### Testing done
CI

#### License

- [x] By submitting this pull request, I confirm that my contribution is
made under the terms of the [Apache 2.0
license](https://pasteurlabs.github.io/tesseract/LICENSE).
- [x] I sign the Developer Certificate of Origin below by adding my name
and email address to the `Signed-off-by` line.

<details>
<summary><b>Developer Certificate of Origin</b></summary>

```text
Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
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```

</details>

Signed-off-by: Dion Häfner <dion.haefner@simulation.science>

Author: dionhaefner

tesseract_core/sdk/cli.py

@@ -272,6 +272,9 @@ def build_image(
 
     The passed directory must contain the files `tesseract_api.py` and `tesseract_config.yaml`
     (can be created via `tesseract init`).
+
+    Prints the built images as JSON array to stdout, for example: `["mytesseract:latest"]`.
+    If `--generate-only` is set, the path to the build context is printed instead.
     """
     if config_override is None:
         config_override = []
@@ -313,6 +316,7 @@ def build_image(
         # output is the built image
         image = build_out
         logger.info(f"Built image {image.short_id}, {image.tags}")
+        typer.echo(json.dumps(image.tags))
 
 
 @app.command("init")

tests/endtoend_tests/common.py

@@ -1,6 +1,7 @@
 # Copyright 2025 Pasteur Labs. All Rights Reserved.
 # SPDX-License-Identifier: Apache-2.0
 
+import json
 import traceback
 
 from typer.testing import CliRunner
@@ -27,7 +28,7 @@ def print_debug_info(result):
 
 
 def build_tesseract(sourcedir, image_name, tag=None, build_retries=3):
-    cli_runner = CliRunner()
+    cli_runner = CliRunner(mix_stderr=False)
 
     build_args = [
         "--loglevel",
@@ -58,4 +59,7 @@ def build_tesseract(sourcedir, image_name, tag=None, build_retries=3):
 
     print_debug_info(result)
     assert result.exit_code == 0, result.exception
-    return image_name
+
+    image_tags = json.loads(result.stdout.strip())
+    assert image_name in image_tags
+    return image_tags[0]