feat: CLI v2.1.81 features + global CLAUDE.md editor (#263)

## Summary

Implements support for Claude Code CLI v2.1.81 features and adds a global CLAUDE.md editor, closing issues #237, #239, #244, #245, #246, #247, #248, and #262.

### Stream-JSON forward-compatibility (#245, #246, #247, #248)

- **#248** — `output_style` field added to `System` init message; silently accepted for forward-compat
- **#245** — `fast_mode_state` field added to `Result` message; logged at debug level
- **#246** — `model_usage` field added to `Result` message; per-model breakdown logged at debug level
- **#247** — `total_cost_usd` field added to `Result` message; authoritative cost logged at debug level

### New config options (#237, #239, #244)

- **#237** — `bare_mode` config toggle: passes `--bare` to Claude Code, suppressing UI chrome for scripted headless `-p` calls
- **#239** — `show_clear_context_on_plan_accept` toggle: passes `showClearContextOnPlanAccept: false` in `--settings` when disabled
- **#244** — `custom_model_option` text field: sets `ANTHROPIC_CUSTOM_MODEL_OPTION` env var for custom model providers

### Global CLAUDE.md editor (#262)

- New Tauri commands `get_global_claude_md` / `save_global_claude_md` read/write `~/.claude/CLAUDE.md` (creates file + directory if absent)
- New "Global Instructions" section in the Config Sidebar with a textarea and Save button

### Bug fix (pre-existing)

`disable_cron` and `disable_skill_shell_execution` were saved to `HikariConfig` but never passed to `start_claude` invocations — fixed in all 9 call sites. All 3 new config fields are also wired through all 9 call sites.

All changes pass `check-all.sh` (ESLint → Prettier → svelte-check → Vitest → Clippy → cargo test with llvm-cov).

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #263
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src-tauri/src/types.rs

@@ -95,6 +95,9 @@ pub enum ClaudeMessage {
         cwd: Option<String>,
         #[serde(default)]
         tools: Option<Vec<String>>,
+        /// Output style hint from Claude Code (v2.1.81+). Informational only.
+        #[serde(default)]
+        output_style: Option<String>,
     },
     #[serde(rename = "assistant")]
     Assistant {
@@ -119,6 +122,15 @@ pub enum ClaudeMessage {
         permission_denials: Option<Vec<PermissionDenial>>,
         #[serde(default)]
         usage: Option<UsageInfo>,
+        /// Fast mode state from Claude Code v2.1.81+. Values: "default" | "enabled" | "disabled".
+        #[serde(default)]
+        fast_mode_state: Option<String>,
+        /// Per-model usage breakdown from Claude Code v2.1.81+.
+        #[serde(default)]
+        model_usage: Option<serde_json::Value>,
+        /// Authoritative total cost in USD reported by Claude Code v2.1.81+.
+        #[serde(default)]
+        total_cost_usd: Option<f64>,
     },
     #[serde(rename = "rate_limit_event")]
     RateLimitEvent {
@@ -910,4 +922,67 @@ mod tests {
         assert!(!serialized.contains("reason"));
         assert!(!serialized.contains("conversation_id"));
     }
+
+    #[test]
+    fn test_system_init_with_output_style() {
+        let json = r#"{"type":"system","subtype":"init","session_id":"sess-1","output_style":"auto"}"#;
+        let msg: ClaudeMessage = serde_json::from_str(json).unwrap();
+        if let ClaudeMessage::System { output_style, .. } = msg {
+            assert_eq!(output_style, Some("auto".to_string()));
+        } else {
+            panic!("Expected System variant");
+        }
+    }
+
+    #[test]
+    fn test_system_init_without_output_style() {
+        let json = r#"{"type":"system","subtype":"init","session_id":"sess-1"}"#;
+        let msg: ClaudeMessage = serde_json::from_str(json).unwrap();
+        if let ClaudeMessage::System { output_style, .. } = msg {
+            assert!(output_style.is_none());
+        } else {
+            panic!("Expected System variant");
+        }
+    }
+
+    #[test]
+    fn test_result_message_with_fast_mode_state() {
+        let json = r#"{"type":"result","subtype":"success","fast_mode_state":"enabled"}"#;
+        let msg: ClaudeMessage = serde_json::from_str(json).unwrap();
+        if let ClaudeMessage::Result { fast_mode_state, .. } = msg {
+            assert_eq!(fast_mode_state, Some("enabled".to_string()));
+        } else {
+            panic!("Expected Result variant");
+        }
+    }
+
+    #[test]
+    fn test_result_message_with_total_cost_usd() {
+        let json = r#"{"type":"result","subtype":"success","total_cost_usd":0.05}"#;
+        let msg: ClaudeMessage = serde_json::from_str(json).unwrap();
+        if let ClaudeMessage::Result { total_cost_usd, .. } = msg {
+            assert!((total_cost_usd.unwrap() - 0.05).abs() < f64::EPSILON);
+        } else {
+            panic!("Expected Result variant");
+        }
+    }
+
+    #[test]
+    fn test_result_message_without_new_fields() {
+        let json = r#"{"type":"result","subtype":"success"}"#;
+        let msg: ClaudeMessage = serde_json::from_str(json).unwrap();
+        if let ClaudeMessage::Result {
+            fast_mode_state,
+            model_usage,
+            total_cost_usd,
+            ..
+        } = msg
+        {
+            assert!(fast_mode_state.is_none());
+            assert!(model_usage.is_none());
+            assert!(total_cost_usd.is_none());
+        } else {
+            panic!("Expected Result variant");
+        }
+    }
 }