feat(agents): fix CLI provider invocations and add streaming output support (F078)

[pocky]

Summary

• Fix CLI invocation flags for all 4 providers to match current binary APIs: Claude/Gemini --output-format json → stream-json, Codex --prompt/--quiet → exec --json <prompt>, OpenCode gains --format json and --model support
• Add stdout, stderr io.Writer parameters to Execute and ExecuteConversation in the ports interface and all provider implementations, enabling streaming output propagation
• Remove dead validation helpers (validatePrompt, validateContext, validateState, validateCodexOptions) that became no-ops after previous provider refactoring

Changes

Ports / Interface

• internal/domain/ports/agent_provider.go: Add stdout, stderr io.Writer params to Execute and ExecuteConversation signatures
• internal/domain/ports/agent_provider_test.go: Update interface tests for new signature
• internal/domain/ports/cli_executor.go: Propagate writer params through CLI executor abstraction
• internal/domain/ports/cli_executor_test.go: Update tests

Provider Implementations

• internal/infrastructure/agents/claude_provider.go: Map output_format: json → --output-format stream-json; accept stream-json pass-through; wire stdout/stderr writers
• internal/infrastructure/agents/codex_provider.go: Migrate from --prompt/--quiet to exec --json <prompt>; resume from codex resume <id> --prompt to codex resume <id> --json; remove quiet option
• internal/infrastructure/agents/gemini_provider.go: Map output_format: json → --output-format stream-json; wire writers
• internal/infrastructure/agents/opencode_provider.go: Add --format json always-on flag and --model option support; wire writers
• internal/infrastructure/agents/openai_compatible_provider.go: Update signature to accept stdout/stderr writers
• internal/infrastructure/agents/cli_executor.go: Wire writer params through CLI execution
• internal/infrastructure/agents/helpers.go: Remove dead validation helpers (validatePrompt, validateContext, validateState)
• internal/infrastructure/agents/options.go: Add output_format / quiet option declarations

Application Layer

• internal/application/conversation_manager.go: Thread stdoutW, stderrW io.Writer through executeTurn and ExecuteConversation
• internal/application/execution_service.go: Pass writers through agent step and conversation execution

Mocks & Test Infrastructure

• internal/testutil/mocks/mocks.go: Update MockAgentProvider to match new Execute/ExecuteConversation signatures
• internal/testutil/mocks/mocks_agent_test.go: Update mock tests
• internal/testutil/mocks/mocks_cli_executor_test.go: Update CLI executor mock tests

Tests

• internal/infrastructure/agents/claude_provider_stream_json_test.go (new): Tests for stream-json output format flag mapping
• internal/infrastructure/agents/codex_provider_exec_test.go (new): Tests for codex exec --json invocation
• internal/infrastructure/agents/codex_provider_resume_test.go (new): Tests for codex resume --json conversation resume
• internal/infrastructure/agents/claude_provider_unit_test.go: Extend unit tests for new flag behavior
• internal/infrastructure/agents/codex_provider_unit_test.go: Extend unit tests; remove quiet option tests
• internal/infrastructure/agents/codex_provider_model_unit_test.go: Trim tests no longer applicable after exec migration
• internal/infrastructure/agents/codex_provider_session_test.go: Update session tests for resume flag change
• internal/infrastructure/agents/gemini_provider_unit_test.go: Extend tests for stream-json mapping
• internal/infrastructure/agents/gemini_provider_session_test.go: Update session tests
• internal/infrastructure/agents/opencode_provider_unit_test.go: Extend tests for --format json and --model
• internal/infrastructure/agents/opencode_provider_session_test.go: Update session tests
• internal/infrastructure/agents/openai_compatible_provider_test.go: Update for new signature
• internal/infrastructure/agents/openai_compatible_provider_unit_test.go: Update unit tests
• internal/infrastructure/agents/helpers_test.go: Remove tests for deleted helpers
• internal/infrastructure/agents/cli_executor_test.go: Update for writer params
• internal/infrastructure/agents/mock_provider.go: Update mock to new interface
• internal/infrastructure/agents/mock_provider_test.go: Update mock tests
• internal/infrastructure/agents/provider_options_test.go: Update option validation tests
• internal/infrastructure/agents/registry_test.go: Minor updates
• internal/application/agent_step_test.go: Update all SetExecuteFunc callbacks to new signature
• internal/application/conversation_manager.go: Already covered above
• internal/application/conversation_manager_helpers_test.go: Update internal mock to new interface
• internal/application/conversation_manager_test.go: Pass nil, nil writers in all ExecuteConversation calls
• internal/application/execution_service_conversation_step_test.go (renamed from t009): Rename for clarity
• internal/application/execution_service_conversation_test.go: Minor updates
• internal/application/execution_service_dangerous_skip_audit_test.go: Minor updates
• internal/application/execution_service_hooks_test.go: Minor updates
• internal/application/execution_service_json_field_mapping_test.go: Minor updates
• internal/application/execution_service_output_format_test.go: Update for new stream-json mapping
• tests/integration/execution/provider_interpolation_test.go: Minor updates

Documentation

• CHANGELOG.md: Document F078 breaking changes (flag migrations, removed quiet option) and additions (OpenCode --model, --format json)
• CLAUDE.md: Add architecture rule to synchronize provider CLI flag changes with options.go; remove stale review section

Test plan

• Run unit tests: make test-unit — all provider flag-construction tests pass
• Verify Codex invocation builds exec --json <prompt> and resume builds codex resume <id> --json <prompt>: check codex_provider_exec_test.go and codex_provider_resume_test.go
• Verify Claude/Gemini output_format: json in a workflow YAML produces --output-format stream-json in the CLI command: check claude_provider_stream_json_test.go
• Run full test suite with race detector: make test-race

Closes #301

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