Remove legacy Codebox ability aliases

[chubes4]

Summary

• Remove legacy public ability alias registration for the run-sandbox-task family.
• Remove browser ability descriptor aliases for create-sandbox-session, create-task-contract, and open-contained-runtime.
• Keep canonical Codebox abilities registered and update tests/docs/runtime manifest to assert the canonical surface.

Tests

• npm run build
• npm run test:public-ability-aliases
• npm run test:runtime-contract-manifest
• npm run test:php-public-api-facade
• npm run test:wordpress-plugin-public-runtime-abilities

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode
• Used for: Searching alias usage, editing code/tests/docs, running focused verification, and drafting this PR description.