feat: add clx health command with 9 system validators

[blackaxgit]

Summary

Add clx health command that checks all CLX components and reports status with actionable fix hints.

Example Output

CLX Health Check (v0.2.1)
══════════════════════════════════════════════════

✓ Configuration     ~/.clx/config.yaml loaded (sensitivity: standard)
✓ Database          ~/.clx/data/clx.db (WAL, schema v4, 2.4MB)
✓ sqlite-vec        built-in (statically linked)
✓ Ollama service    http://127.0.0.1:11434 reachable (42ms)
✓ Validator model   qwen3:1.7b available
✓ Embedding model   qwen3-embedding:0.6b available
✓ Hook binary       ~/.clx/bin/clx-hook
✓ MCP binary        ~/.clx/bin/clx-mcp
✓ Validator prompt  standard (built-in)

══════════════════════════════════════════════════
All checks passed (9/9)

Failures show fix hints:

✗ Ollama service    http://127.0.0.1:11434 unreachable
                    → Start Ollama: ollama serve

Features

• 9 concurrent validators (config, DB, sqlite-vec, Ollama, 2 models, 2 binaries, prompt)
• --json flag for scripting
• Exit code 0 (healthy) / 1 (any failure)
• Actionable fix hints on failures
• No new dependencies

Files Changed

File	Change
crates/clx/src/commands/health.rs	NEW: 729 lines, 9 validators + output formatting + 10 tests
crates/clx/src/commands/mod.rs	Add pub mod health
crates/clx/src/main.rs	Add Health subcommand with --json flag
crates/clx-core/src/policy/llm.rs	Widen load_validator_prompt to pub
crates/clx-core/src/policy/mod.rs	Re-export load_validator_prompt

Test Plan

• 159 tests pass in clx crate (128 unit + 31 integration)
• 0 clippy warnings
• Manual test: table output with Ollama down (shows failures + hints)
• Manual test: JSON output parses correctly
• Exit code 1 when checks fail, 0 when all pass