feat: add env variables properly and proper documentations

[dinahmaccodes]

PR Description

This PR fixes documentation inconsistencies, deployment script issues, adds CI size budget enforcement, and configures code ownership for review routing.

Changes:

• Fixed environment variable names in ARCHITECTURE.md to match backend code (STREAM_CONTRACT_ID, lowercase STELLAR_NETWORK)
• Fixed deploy.sh to prevent clobbering exported environment variables with empty defaults
• Added WASM size budget check (200KB) to CI workflow to prevent size regressions
• Added CODEOWNERS file for automatic PR review assignment

Checklist:

• Fixed [Docs] ARCHITECTURE.md documents wrong backend env var name (STREAMING_CONTRACT_ADDRESS vs STREAM_CONTRACT_ID) #900 - Updated docs/ARCHITECTURE.md env var names (STREAM_CONTRACT_ID, lowercase STELLAR_NETWORK)
• Fixed [Infra] scripts/deploy.sh clobbers all required env vars with empty defaults, so deployment always aborts #887 - Fixed scripts/deploy.sh env var clobbering issue
• Fixed [CI] Contracts CI optimizes WASM but enforces no size budget (no wasm-size gate) #896 - Added WASM size budget check to CI workflow with 200KB limit
• Fixed [Chore] Add .github/CODEOWNERS for review routing #904 - Added .github/CODEOWNERS file for review routing
• All changes committed with proper commit messages
• Changes pushed to branch issuenew

Closes:
Closes #900
Closes #887
Closes #896
Closes #904