feat: finalize phase 7 hexagonal boundaries and add technical architecture patterns

[Lythaeon]

Summary

• Finalize Phase 7 hexagonal boundaries so orchestration is entry -> application -> adapters, with runtime slices invoked through ports.
• Eliminate remaining non-test cross-slice imports and tighten architecture guardrails.
• Expand stability/fault/aggregation validation coverage.
• Replace migration-era architecture docs with current-flow docs and add technical docs in ARD/ADR/patterns.

Changes

• Boundary/seam finalization:
  • Introduced runtime adapter seam in src/adapters/runtime/ and wired application orchestration through it.
  • Added src/application/slice_execution.rs to make application the explicit orchestrator for local/replay/compare/cleanup/service flows.
  • Decoupled distributed agent execution from application-local types via AgentLocalRunPort/AgentRunOutcome contracts.
  • Removed remaining non-test direct cross-slice imports.
• Guardrails:
  • Extended scripts/check_architecture.sh rules so:
    • application cannot import app or distributed
    • distributed cannot import app or application
    • entry cannot import app, distributed, or service
• Tests added:
  • Distributed soak stability
  • Auth-token mismatch fault behavior
  • Controller event fault handling (disconnect/mismatch/decode)
  • Aggregation dedup + high-cardinality behavior
• Documentation:
  • Simplified docs/architecture/ard/ARCHITECTURE_OVERVIEW.md to current mode-by-mode call flows.
  • Removed legacy ARD docs:
    • docs/architecture/ard/ARCHITECTURE_RISKS_HEXAGONAL_PLAN.md
    • docs/architecture/ard/ARCHITECTURE_BASELINE_METRICS.md
  • Added technical docs:
    • ARD: docs/architecture/ard/ARCHITECTURE_TECHNICAL_GUIDE.md
    • ADR: docs/architecture/adr/ADR-0002-type-safety-dispatch-concurrency.md
    • Patterns: docs/architecture/patterns/type-safety-performance-concurrency.md
  • Updated architecture/doc indexes and changelog entries to match final structure.

Checks

• cargo make format
• cargo make clippy
• cargo make test (203/203)
• cargo make architecture-check