feat: enable standalone UI in docker-compose with configurable deployment mode

[ederign]

Description

Add deployment mode and style theme as parameters to the UI Dockerfile, enable --mock-k8s-client=true for standalone mode, and integrate the UI service into docker-compose for running the complete local development stack.
Closes #2055 .

Changes

• Add DEPLOYMENT_MODE and STYLE_THEME as build arguments to UI Dockerfile
• Enable --mock-k8s-client=true in the standalone Docker image
• Add model-registry-ui service to docker-compose.yaml (pre-built images)
• Add model-registry-ui service to docker-compose-local.yaml (builds from source)
• Use extra_hosts: localhost:host-gateway to route BFF connections to model-registry and model-catalog containers

After PR review:

• Create dedicated Dockerfile.standalone with envtest support to avoid
  bloating production image with K8s test binaries (~150MB)
• Keep main Dockerfile clean for kubeflow/federated deployments
• Update docker-compose.yaml to use ui-standalone image
• Add explicit --mock-mr-client=false and --mock-mr-catalog-client=false
  flags for better readability
• Update Makefile and GitHub workflow to use new Dockerfile
• Document Dockerfile structure in README

Usage

# Using pre-built images
make compose/up/postgres

**Endpoints:**
- UI: http://localhost:9000
- Model Registry: http://localhost:8080
- Model Catalog: http://localhost:8081

# Building from source
make compose/local/up/postgres

How Has This Been Tested?

Verified UI successfully fetches data from both model-registry and model-catalog via the host-gateway routing.
make compose/local/up/postgres
make compose/up/postgres

Kapture.2026-01-03.at.13.03.17.mp4

Merge criteria:

• All the commits have been signed-off (To pass the DCO check)

• The commits have meaningful messages
• [ ]Automated tests are provided as part of the PR for major new functionalities; testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work.
• Code changes follow the kubeflow contribution guidelines.
• For first time contributors: Please reach out to the Reviewers to ensure all tests are being run, ensuring the label ok-to-test has been added to the PR.

[ederign]

@tarilabs better late than never 😅

[lucferbux]

A couple of nits but there's the part of adding env-test to the dockerfile, we should avoid that at all costs, maybe we might wanna explore having an extra dockerfile or smth similar.

[ederign]

@lucferbux ready for another round!

[lucferbux]

/lgtm
/approve

[ederign]

@tarilabs, when you have a chance, could you please take a look at it?

[tarilabs]

thanks a lot @ederign and @lucferbux

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lucferbux, tarilabs

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