feat(agents): add human-readable streaming display for agent steps (F082)

[pocky]

Summary

• Add human-readable streaming display for agent steps (F082): when running with --output streaming or --output buffered, agent NDJSON responses are filtered to plain text instead of showing raw wire format
• The output_format field now serves dual purpose — post-processing (code fence stripping) AND terminal display routing: text/omitted filters to readable output, json passes raw NDJSON through
• DisplayOutput field propagates from AgentResult through ConversationResult → StepState → CLI summary; state.Output retains raw NDJSON for template interpolation unchanged
• cloneAndInjectOutputFormat now normalizes OutputFormatNone → text so the display-matrix pipeline always receives an explicit format value, and is applied consistently to both executeAgentStep and ExecuteConversation paths

Changes

Infrastructure — Agent Providers

• internal/infrastructure/agents/base_cli_provider.go: Wire parseStreamLine hook into streaming I/O path; apply streamFilterWriter when output_format is not json; populate DisplayOutput in returned AgentResult
• internal/infrastructure/agents/stream_filter.go: Simplify streamFilterWriter — remove redundant buffering logic, tighten LineExtractor contract
• internal/infrastructure/agents/opencode_provider.go: Add stub parseStreamLine hook to satisfy updated cliProviderHooks struct

Application Layer

• internal/application/execution_service.go: Normalize OutputFormatNone → OutputFormatText in cloneAndInjectOutputFormat so downstream always sees an explicit value
• internal/application/conversation_manager.go: Replace inline options map construction with cloneAndInjectOutputFormat to apply identical display routing to conversation turns (F082 cross-path consistency)

Tests

• internal/application/execution_service_display_output_test.go: Add table-driven tests for output_format injection (text/json/none→text), nil-options handling, and option map immutability (FR-009)
• internal/infrastructure/agents/claude_provider_display_output_unit_test.go: Refocus tests on parseClaudeStreamLine extraction; remove obsolete streaming-path tests superseded by base provider
• internal/infrastructure/agents/opencode_provider_display_output_unit_test.go: Update to reflect stub extractor behavior after OpenCode gains parseStreamLine hook
• internal/infrastructure/agents/stream_filter_unit_test.go: Align with simplified streamFilterWriter contract; add benchmark for throughput and 1 MB buffer constraint
• internal/domain/workflow/context_json_test.go: Assert DisplayOutput is NOT resolvable in template interpolation context (prevents accidental exposure)
• internal/interfaces/cli/run.go: Remove unused import/variable introduced during earlier wiring
• pkg/interpolation/resolver_data_test.go: Add DisplayOutput to excluded-fields coverage
• tests/integration/agents/f082_display_matrix_test.go: New integration test matrix covering all provider × output-mode × output-format combinations

Documentation

• docs/user-guide/agent-steps.md: Add Streaming Output Display section with mode/format matrix table and examples for streaming, buffered, and silent modes
• docs/user-guide/commands.md: Update --output flag table to document agent-step display filtering behavior
• docs/README.md: Add link to new Streaming Output Display subsection
• README.md: Update feature bullet to mention human-readable streaming display
• CHANGELOG.md: Add F082 entry under Added

Project Config

• CLAUDE.md: Add architecture rules for cross-path hook wiring and test conventions for DisplayOutput field isolation and benchmark requirements; remove stale rules

Test plan

• make test — all unit and integration tests pass including new f082_display_matrix_test.go
• awf run <workflow-with-agent-step> --output streaming — terminal shows readable text, not raw {"type":"content_block_delta",...} NDJSON
• awf run <workflow-with-agent-step> --output streaming with output_format: json — raw NDJSON appears unchanged on terminal
• Template interpolation {{states.step.display_output}} returns empty/unresolved — DisplayOutput is not exposed to workflows

Closes #311

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