feat: customizable validator prompt with sensitivity presets

[blackaxgit]

Summary

Add customizable LLM validator prompts with 3 sensitivity presets and per-project override support.

How It Works

Prompt Resolution (highest priority wins):

  1. Per-project:  <project>/.clx/prompts/validator.txt
  2. Global:       ~/.clx/prompts/validator.txt
  3. Built-in:     Preset based on config (high/standard/low)

Sensitivity Presets

Preset	Behavior	Best For
high	Flags network access, env vars, file writes outside project, package installs	Production, corporate compliance
standard	Balanced risk assessment (current default)	General development
low	Trusts common dev tools (npm, cargo, docker, git), only flags destructive ops	Personal projects, rapid prototyping

Config

validator:
  prompt_sensitivity: standard  # high | standard | low | custom

Per-Project Override

mkdir -p .clx/prompts
cp ~/.clx/prompts/validator-high.txt .clx/prompts/validator.txt

Files Changed

File	Change
crates/clx-core/src/policy/prompts/	NEW: 3 template files (high, standard, low)
crates/clx-core/src/policy/prompts.rs	NEW: module embedding templates via include_str!
crates/clx-core/src/policy/llm.rs	3-tier prompt loading (per-project > global > built-in)
crates/clx-core/src/config.rs	PromptSensitivity enum + config field
crates/clx-hook/src/hooks/pre_tool_use.rs	Pass sensitivity to evaluate_with_llm
crates/clx/src/commands/install.rs	Write all 3 templates + active prompt during install

Test Plan

• All workspace tests pass
• 0 clippy warnings
• Prompt loading precedence tested (per-project > global > built-in)
• Sensitivity deserialization tested
• Existing validation (injection detection) still applies to all prompts
• Backward compatible -- standard preset matches previous behavior