refactor(arch): extract persistence codec and domain types to proper layers

[pocky]

Summary

• Refactor persistence codec from infrastructure/persistence/encoder.zig into application/persistence_codec.zig, enforcing strict hexagonal layer separation by keeping encode/decode logic out of I/O adapters
• Introduce PersistencePort vtable interface and make Scheduler generic via SchedulerWith(comptime Backend: type) to decouple the application layer from concrete persistence backends
• Promote domain-level types (timestamp.zig, shell_config.zig, telemetry_config.zig) and OTel instruments (instruments.zig) to their correct layers; extract shared subprocess spawn logic into runner/subprocess.zig
• Fix ExecutionClient memory ownership: dupe job identifier strings at trigger time, propagate resolve() errors instead of silently discarding them, and switch all unit tests to std.testing.allocator for leak detection

Changes

Application Layer

• src/application.zig: Export new persistence_codec and instruments modules
• src/application/persistence_codec.zig: New — full encode/decode for all entry types (job, rule, removals, all 6 runner variants) with errdefer-safe allocation and comprehensive unit tests
• src/application/persistence_port.zig: New — vtable-based PersistencePort interface decoupling Scheduler from concrete backend
• src/application/instruments.zig: New — OTel Instruments struct promoted from infrastructure into application layer
• src/application/execution_client.zig: Dupe job_identifier at trigger(), make resolve() return !void, fix pull_results to free owned identifiers, switch tests to std.testing.allocator
• src/application/job_storage.zig: Replace linear scan + sort in get_to_execute with priority-queue peek/remove; add count() and count_by_status() accessors; switch tests to std.testing.allocator
• src/application/query_handler.zig: Update to use new persistence port and codec interfaces
• src/application/rule_storage.zig: Minor updates for layer alignment
• src/application/scheduler.zig: Make generic via SchedulerWith(comptime Backend: type); wire through new persistence port
• src/application/token_store.zig: Layer alignment cleanup

Domain Layer

• src/domain.zig: Export new domain modules
• src/domain/shell_config.zig: New — ShellConfig type promoted from infrastructure
• src/domain/telemetry_config.zig: New — TelemetryConfig type promoted from infrastructure
• src/domain/timestamp.zig: New — Timestamp parsing/formatting promoted from infrastructure
• src/domain/auth.zig: Layer alignment
• src/domain/job.zig: Minor fix
• src/domain/query.zig: Update query types for new layer structure
• src/domain/runner.zig: Minor alignment
• src/domain/server_stats.zig: Reduced — fields delegated to proper domain types

Infrastructure Layer

• src/infrastructure/persistence/encoder.zig: Gutted — logic moved to application/persistence_codec.zig; now thin adapter delegating to codec
• src/infrastructure/persistence/backend.zig: Updated to use PersistencePort and application-layer codec
• src/infrastructure/persistence/background.zig: Updated for new codec/port interfaces
• src/infrastructure/persistence/logfile.zig: Minor update
• src/infrastructure/runner/subprocess.zig: New — extracted shared subprocess spawn logic used by shell, direct, awf runners
• src/infrastructure/shell_runner.zig: New — shell runner adapter using new subprocess module
• src/infrastructure/runner/shell.zig: Delegate to subprocess.zig
• src/infrastructure/runner/direct.zig: Delegate to subprocess.zig
• src/infrastructure/runner/awf.zig: Minor update
• src/infrastructure/runner.zig: Barrel update
• src/infrastructure/clock.zig: Minor alignment
• src/infrastructure/http.zig: Layer alignment
• src/infrastructure/http/json.zig: Layer alignment
• src/infrastructure/protocol/parser.zig: Minor update
• src/infrastructure/tcp_server.zig: Update for new scheduler generic type
• src/infrastructure/telemetry.zig: Use application/instruments.zig types
• src/infrastructure/tls_context.zig: Minor update

Interfaces & Entry Point

• src/interfaces/cli.zig: Update for new scheduler type
• src/interfaces/config.zig: Use promoted domain config types
• src/interfaces/dump.zig: Update for new codec location
• src/main.zig: Wire SchedulerWith generic, thread updates for new layer structure

Tests & Docs

• src/functional_tests.zig: Extended test coverage for refactored paths
• functional_tests: Compiled functional test binary (should be in .gitignore)
• CHANGELOG.md: Document hexagonal architecture refactoring under [Unreleased]
• CLAUDE.md: Expanded with Performance Principles, Memory & Allocators, Zig 0.15.2 Idioms, Hot Paths, Observability, and additional review/pitfall rules

Test plan

• make build compiles without errors or warnings
• zig build test-all passes all layer-specific unit tests including new persistence_codec tests
• zig build test-functional passes end-to-end scheduler round-trip (SET job → tick → execute → persist → reload)
• Run sanitizer targets: zig build test-asan and zig build test-tsan report no heap or data-race errors

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