refactor: migrate monolithic crate to Cargo Workspace with Clean Architecture

Transform the single binary crate into a 9-crate workspace monorepo:

- Root Cargo.toml as [workspace] manager with resolver = "2"
- zesdex-entities: Domain entity types (session, settings, store, message, etc.)
- zesdex-utils: Pure utility functions (error, logger, pagination, slug, clipboard)
- zesdex-dto: Data Transfer Objects for LLM provider API communication
- zesdex-ipc: Unix-socket IPC layer (client/server/framing/protocol)
- zesdex-iam: Identity & Access Management (Clean Architecture: domain/application/infrastructure)
- zesdex-cms: Content Management (Clean Architecture: domain/application/infrastructure)
- zesdex-middleware: HTTP middleware (Auth, CORS, Rate Limiting)
- zesdex-libs: Composition root (AppContext, DB init, JWT, Argon2)
- zesdex-backend: Main binary entry point + seed/migrate binaries
- DevOps: Dockerfile, docker-compose, Nix (flake/shell/default), CI/CD updates
- Remove dead root src/ and src-misc/ directories

All crate re-exports maintain backward compatibility with original
crate::model::*, crate::dto::*, crate::ipc::* module paths.
Feature crates enforce strict layer separation: domain -> application
-> infrastructure with generic trait-based dependency injection.

crates/zesdex-cms/src/domain/settings.rs

@@ -0,0 +1,88 @@
+//! Pure Settings entity — user configuration for LLM provider, model,
+//! generation parameters, and feature flags.
+//!
+//! # Architecture
+//! This is a pure data structure with **no I/O logic**.  Load/save
+//! responsibilities live in [`SettingsRepository`](super::repository::SettingsRepository).
+
+#![allow(
+    clippy::cast_possible_truncation,
+    clippy::cast_sign_loss,
+    clippy::cast_precision_loss,
+    clippy::cast_possible_wrap
+)]
+
+use std::collections::HashMap;
+
+use serde::{Deserialize, Serialize};
+
+/// Controls how much network access the agent is permitted during a session.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, Default)]
+pub enum InternetMode {
+    #[default]
+    Off,
+    ReadOnly,
+    Full,
+}
+
+/// Boolean flags grouped to keep the top-level [`Settings`] struct below
+/// clippy's default-too-many-fields threshold.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SettingsFlags {
+    pub review_enabled: bool,
+    pub session_archive_enabled: bool,
+    pub lsp_auto_provision: bool,
+}
+
+impl Default for SettingsFlags {
+    fn default() -> Self {
+        Self {
+            review_enabled: true,
+            session_archive_enabled: true,
+            lsp_auto_provision: true,
+        }
+    }
+}
+
+/// Top-level application settings.
+///
+/// Serialized to `settings.json` by the infrastructure layer.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Settings {
+    pub internet_mode: InternetMode,
+    pub provider: String,
+    pub model: String,
+    pub api_keys: HashMap<String, String>,
+    pub max_tokens: Option<u32>,
+    pub temperature: Option<f32>,
+    pub review_max_lessons_per_run: usize,
+    pub adaptive_review_max_skip: u32,
+    pub verify_command: Option<String>,
+    pub verify_timeout_ms: u64,
+    pub workflow_max_concurrency: usize,
+    #[serde(flatten)]
+    pub flags: SettingsFlags,
+    pub lsp_languages: Vec<String>,
+    pub hive_mind_node_timeout_ms: u64,
+}
+
+impl Default for Settings {
+    fn default() -> Self {
+        Self {
+            internet_mode: InternetMode::Off,
+            provider: "zen".to_string(),
+            model: "deepseek-v4-flash-free".to_string(),
+            api_keys: HashMap::new(),
+            max_tokens: None,
+            temperature: None,
+            review_max_lessons_per_run: 5,
+            adaptive_review_max_skip: 3,
+            verify_command: None,
+            verify_timeout_ms: 30_000,
+            workflow_max_concurrency: 5,
+            flags: SettingsFlags::default(),
+            lsp_languages: Vec::new(),
+            hive_mind_node_timeout_ms: 600_000,
+        }
+    }
+}