Fix agentic-atx-platform deployment + stale transform IDs; default to Claude Sonnet 4.5

[syepesaws]

Description

Fixes that unblock deploying the agentic-atx-platform sample and align it with the current AWS Transform registry.

1. CDK: honor useBaseInfra context + optional prebuilt image (cdk/bin/cdk.ts)

• useBaseInfra was hardcoded as === 'true' || true, which always evaluates to true. This forced hybrid mode and meant the full-mode stacks (AtxContainerStack, AtxInfrastructureStack) documented in README Option A/B were never instantiated. Normalized to accept either a string 'true' or a JSON boolean true.
• Added an optional -c publicEcrImage=<uri> context flag. When set, the local Docker build is skipped and the Batch job uses the prebuilt image (e.g. public.ecr.aws/b7y6j9m3/aws-transform-custom:latest). Default behavior is unchanged.

2. Fix stale AWS-managed transformation identifiers (ui/...)

• The Execute form and sample CSVs referenced AWS/early-access-comprehensive-codebase-analysis and AWS/early-access-jfr-performance-optimization, which are not in the ATX registry and fail at atx custom def exec ("Transformation not found").
• Updated to the current names (AWS/comprehensive-codebase-analysis, AWS/java-performance-optimization) and added the missing vue.js-version-upgrade, angular-version-upgrade, and early-access-log4j-to-slf4j-migration, matching findtransform.py/TransformationList.jsx.

3. Default orchestrator model to Claude Sonnet 4.5

• Bumped the default to us.anthropic.claude-sonnet-4-5-20250929-v1:0 across the SAM template default, config.env.template, code fallbacks, and docs.
• sam/deploy.sh now passes BedrockModelId only when explicitly configured, so the SAM template default applies otherwise (no empty override).

Testing

• Deployed end-to-end via Option A (CDK + SAM) in us-east-1: infrastructure, AgentCore runtime (READY), HTTP API, and CloudFront UI.
• Verified the UI loads, /orchestrate responds, and a transformation submits to AWS Batch with a valid registry identifier.
• tsc compiles cleanly; bash -n passes on deploy.sh.

Notes / follow-ups

• The UI transformation list is still hardcoded (now consistent across the repo). Consolidating it behind a single backend endpoint is a reasonable follow-up but out of scope here.
• package-lock.json files are intentionally not included.

Licensing

By submitting this PR, I confirm my contribution is made under the terms of the project's MIT-0 license.