feat: add zeroclaw config schema for JSON Schema export

Add a `config schema` subcommand that dumps the full configuration
schema as JSON Schema (draft 2020-12) to stdout. This enables
downstream consumers (like PankoAgent) to programmatically validate
configs, generate forms, and stay in sync with zeroclaw's evolving
config surface without hand-maintaining copies of the schema.

- Add schemars 1.2 dependency and derive JsonSchema on all config
  structs/enums (schema.rs, policy.rs, email_channel.rs)
- Add `Config` subcommand group with `Schema` sub-command
- Output is valid JSON Schema with $defs for all 56 config types

src/security/policy.rs

@@ -1,10 +1,11 @@
 use parking_lot::Mutex;
+use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use std::path::{Path, PathBuf};
 use std::time::Instant;
 
 /// How much autonomy the agent has
-#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "lowercase")]
 pub enum AutonomyLevel {
     /// Read-only: can observe but not act