Replace runtime snapshot metadata fetch with CI-injected BuildConfig metadata

[hdcodedev]

Problem

The playground footer currently depends on runtime fetch/deserialization of metadata JSON. This creates failure modes from deploy skew, caching, and runtime serialization issues.

Proposal

Replace runtime metadata fetch entirely with CI-injected build-time markers in BuildConfig:

• SOURCE_SHA
• CHARTS_VERSION
• PUBLISHED_AT

Populate them in publish workflow during build.

Non-Goal

• No runtime fallback to metadata endpoint.
• No runtime HTTP fetch for footer metadata.

Why

• Eliminates runtime network dependency for footer
• Eliminates schema drift/parsing issues in UI
• Guarantees metadata matches the exact deployed JS bundle

Suggested Implementation

1. Add BuildConfig fields in playground/build.gradle.kts with explicit local defaults.
2. Pass CI values via Gradle properties/env in publish workflow.
3. Remove metadata fetch from PlaygroundViewModel and related loading state/actions.
4. Render footer directly from BuildConfig values.

Acceptance Criteria

• Footer metadata renders with zero runtime HTTP calls.
• Published snapshot footer always matches deploy commit/version/time.
• Metadata endpoint availability has no effect on footer behavior.