refactor(ai): align multimodal naming

[rekram1-node]

Summary

• rename shared cross-modality failures from LLMError to AIError and move runtime identities from LLM.* to AI.*
• move provider metadata into the shared Schema AI namespace and rebrand shared IDs, HTTP diagnostics, usage, and executor services
• rename the executable language-model Model family to LanguageModel while retaining the conversational LLMRequest / LLMEvent / LLMResponse / LLMClient family
• update providers, Core consumers, tests, examples, and package guidance with no compatibility aliases

Verification

• bun typecheck in packages/schema, packages/ai, packages/core, packages/plugin, and packages/simulation
• bun run build in packages/schema and packages/ai
• 34 focused AI schema/export/image/LLM tests
• 119 OpenAI Chat and Responses tests
• 195 Core runner/resolver/adapter/session tests
• 6 Core shared-schema/session-error tests

Notes

• Full packages/ai replay has two pre-existing OpenRouter reasoning fixture mismatches caused by the current usage.include request shape; all rename-related suites pass.
• Full packages/schema has one pre-existing Agent.Color contract-hygiene failure.
• The unrelated untracked root images.md is excluded.