Modularize agent interpreter provider into focused application modules

[danielbdyer]

Motivation

• Break up the large agent-interpreter-provider implementation into focused, testable pieces to improve separation of concerns, make provider variants pluggable, and enable incremental migration.
• Surface a stable compatibility shim so callers continue to work while the new package is adopted.

Description

• Extracted the agent interpreter implementation into a new package lib/application/agent-interpreter/ with these modules: contract.ts, factory.ts, resilience.ts, ab-testing.ts, and providers/{disabled,heuristic,llm-api,session}.ts to encapsulate provider wiring, retries/timeouts, A/B routing, and concrete providers.
• Added a thin compatibility shim at lib/application/agent-interpreter-provider.ts that re-exports resolveAgentInterpreterProvider, DEFAULT_AGENT_INTERPRETER_CONFIG, resilience helpers, and scoped provider constructors for incremental migration.
• Updated application docs (lib/application/README.md) and regenerated the module map so the new layout is discoverable.
• Added focused tests: tests/agent-interpreter-factory.spec.ts, tests/agent-interpreter-heuristic.spec.ts, tests/agent-interpreter-resilience.spec.ts, and tests/agent-interpreter-provider.integration.spec.ts covering factory precedence, fallback semantics, heuristic determinism, timeout fallback behavior, and an end-to-end LLM parsing integration.

Testing

• Ran npm run map to refresh module discoverability; the command completed successfully.
• Ran targeted Playwright tests for the new modules with npx playwright test against the new interpreter tests and related resilience/resource tests; the newly added tests and the related resource/resilience suites passed (all targeted tests succeeded).
• Ran npm run check; typecheck failed due to pre-existing, unrelated baseline diagnostics in other tests (not introduced by this refactor).

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Codex Task