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/repository.rs

@@ -0,0 +1,76 @@
+//! Repository traits — pure abstraction boundaries for persistence.
+//!
+//! Each trait defines load / save / query operations that infrastructure
+//! adapters implement.  The domain and application layers depend only on
+//! these traits, never on concrete persistence implementations.
+
+#![allow(
+    clippy::cast_possible_truncation,
+    clippy::cast_sign_loss,
+    clippy::cast_precision_loss,
+    clippy::cast_possible_wrap
+)]
+
+use std::path::Path;
+
+use anyhow::Result;
+
+use super::app_config::AppConfig;
+use super::conversation::Conversation;
+use super::edit_log::{EditLog, EditLogEntry};
+use super::memory::Memory;
+use super::settings::Settings;
+
+/// Persistence contract for `Settings`.
+pub trait SettingsRepository {
+    /// Load settings from a base directory.
+    fn load(&self, base_dir: &Path) -> Result<Settings>;
+
+    /// Save settings to a base directory.
+    fn save(&self, base_dir: &Path, settings: &Settings) -> Result<()>;
+}
+
+/// Persistence contract for `AppConfig`.
+pub trait AppConfigRepository {
+    /// Load app config from a base directory.
+    fn load(&self, base_dir: &Path) -> Result<AppConfig>;
+
+    /// Save app config to a base directory.
+    fn save(&self, base_dir: &Path, config: &AppConfig) -> Result<()>;
+}
+
+/// Persistence contract for `Conversation`.
+pub trait ConversationRepository {
+    /// Load a conversation from a session directory.
+    fn load(&self, session_dir: &Path) -> Result<Conversation>;
+
+    /// Save a conversation to a session directory.
+    fn save(&self, session_dir: &Path, conversation: &Conversation) -> Result<()>;
+}
+
+/// Persistence contract for `Memory`.
+pub trait MemoryRepository {
+    /// List all memory slugs in a memory directory.
+    fn list(&self, memory_dir: &Path) -> Result<Vec<String>>;
+
+    /// Load a single memory by name.
+    fn load(&self, memory_dir: &Path, name: &str) -> Result<Memory>;
+
+    /// Save (create or update) a memory.
+    fn save(&self, memory_dir: &Path, memory: &Memory) -> Result<()>;
+
+    /// Delete a memory by name.
+    fn delete(&self, memory_dir: &Path, name: &str) -> Result<()>;
+}
+
+/// Persistence contract for `EditLog`.
+pub trait EditLogRepository {
+    /// Open (or start tracking) the edit log for a session directory.
+    fn open(&self, session_dir: &Path) -> Result<EditLog>;
+
+    /// Append one entry, persisting it immediately.
+    fn append(&self, session_dir: &Path, log: &mut EditLog, entry: EditLogEntry) -> Result<()>;
+
+    /// Return a reference to all in-memory entries.
+    fn entries(&self, log: &EditLog) -> Vec<EditLogEntry>;
+}