Add Claude Code settings infrastructure, TUI mode, session naming, and global defaults

Adds first-class support for Claude Code CLI features (2.1.71-2.1.110):

- New ClaudeCodeSettings struct with per-project and global defaults for
  TUI mode, effort level, focus mode, thinking summaries, session recap,
  auto-scroll, env scrub, and 1-hour prompt caching
- Settings injected as env vars (CLAUDE_CODE_NO_FLICKER, etc.) and
  ~/.claude/settings.json entries via entrypoint.sh merge block
- New ClaudeCodeSettingsModal component for configuring settings
- Session naming support (-n flag passed to claude CLI, shown in tabs)
- Relaxed reserved prefix filter: CLAUDE_CODE_* env vars now allowed in
  custom env vars UI for power users
- Global SSH key path, git name, and git email now used as fallbacks
  when per-project values are not set, with UI in SettingsPanel
- Fingerprint-based change detection triggers container recreation when
  Claude Code settings change
- Updated README, HOW-TO-USE, and CLAUDE.md documentation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src-tauri/src/models/app_settings.rs

@@ -1,6 +1,6 @@
 use serde::{Deserialize, Serialize};
 
-use super::project::EnvVar;
+use super::project::{ClaudeCodeSettings, EnvVar};
 
 fn default_true() -> bool {
     true
@@ -78,6 +78,8 @@ pub struct AppSettings {
     pub web_terminal: WebTerminalSettings,
     #[serde(default)]
     pub stt: SttSettings,
+    #[serde(default)]
+    pub global_claude_code_settings: Option<ClaudeCodeSettings>,
 }
 
 fn default_stt_model() -> String {
@@ -163,6 +165,7 @@ impl Default for AppSettings {
             dismissed_image_digest: None,
             web_terminal: WebTerminalSettings::default(),
             stt: SttSettings::default(),
+            global_claude_code_settings: None,
         }
     }
 }