Add CLI workflow E2E test (init → validate → audit → generate)

[skokaina]

Problem

The critical user journey `init → validate → health → audit → generate` has unit tests per command but no integration test that runs the full sequence. A breaking change in the manifest schema could break the entire flow without CI catching it.

Proposed fix

Add an E2E test (can be a shell script or vitest integration test) that:

1. Runs `agentspec init --yes` in a temp directory
2. Runs `agentspec validate agent.yaml` — asserts exit 0
3. Runs `agentspec health agent.yaml --no-model --no-mcp --no-memory` — asserts exit 0
4. Runs `agentspec audit agent.yaml` — asserts exit 0 and score > 0
5. Runs `agentspec generate agent.yaml --framework langgraph --output ./out/ --dry-run` — asserts exit 0 (dry-run avoids needing ANTHROPIC_API_KEY in CI)

This test should run in CI on every PR.

Acceptance criteria

• E2E test exists and passes locally
• Runs in CI (no external API keys required)
• Covers the happy path a new user follows from the quick-start