refactor: split into Cargo workspace with fine-grained crates + CI/E2E

[loonghao]

Summary

Refactors the monolithic single-crate layout into a clean Cargo workspace with 8 purpose-built crates, adds workspace-hack for build acceleration, automated release versioning via release-please, and a complete CI/E2E testing pipeline.

Workspace Structure

crates/
├── aion-types/      # Shared data types (LLM, message, tool) — zero deps
├── aion-protocol/   # JSON stream protocol events/commands + ToolApprovalManager
├── aion-config/     # Config, ProviderCompat, Auth, Hooks, BedrockConfig, VertexConfig
├── aion-providers/  # LLM provider impls (Anthropic, OpenAI, Bedrock, Vertex)
├── aion-tools/      # Built-in tools (Read, Write, Edit, Bash, Grep, Glob)
├── aion-mcp/        # MCP client (stdio/SSE/HTTP transports)
├── aion-agent/      # AgentEngine, session, spawner, orchestration, output sinks
└── aion-cli/        # CLI binary — thin wrapper over aion-agent
workspace-hack/      # cargo-hakari for build deduplication

Dependency order (no cycles)

aion-types → aion-protocol → aion-config → aion-providers
                           ↘              ↘
                            aion-tools  →  aion-mcp  →  aion-agent  →  aion-cli

CI / Testing

ci.yml — runs on every PR and push to main

• 3-platform matrix: Linux / macOS / Windows
• nextest with --profile ci (parallel, 2× retry, JUnit output)
• cargo-audit security scan
• code coverage on push to main (Codecov)
• JUnit results annotated on PR via dorny/test-reporter

e2e.yml — real API smoke tests

• Triggered on push to main (path-filtered) and workflow_dispatch
• Per-provider matrix: anthropic / openai
• Graceful skip when ANTHROPIC_API_KEY / OPENAI_API_KEY are absent
• Separate nextest profile e2e: sequential, 120 s timeout, no retries
• Tests: single-turn completion + tool-use (Read tool)

release-please.yml — automated versioning

• Two-job design mirroring loonghao/vx to avoid duplicate-PR bug
• Conventional commits → automatic semver bump + CHANGELOG

release.yml — multi-platform binaries

• 8 target platforms (Linux gnu/musl x64/arm64, macOS x64/arm64, Windows x64/arm64)
• Triggered by version tag or workflow_dispatch

Other

• justfile: unified vx just recipes (test, test-ci, test-e2e, check-all, coverage, …)
• .config/nextest.toml: default / ci / e2e profiles
• rust-toolchain.toml: pins stable channel
• Tests migrated to per-crate tests/ directories

Required Secrets

Secret	Purpose
CODECOV_TOKEN	Coverage upload (optional)
ANTHROPIC_API_KEY	E2E Anthropic tests (optional)
OPENAI_API_KEY	E2E OpenAI tests (optional)