feat: initial implementation of content-addressed incremental backup engine

Rust-centric architecture with TypeScript facade following smartproxy/smartstorage pattern.
Core engine in Rust (FastCDC chunking, SHA-256, gzip, AES-256-GCM + Argon2id, binary pack files,
global index, snapshots, locking, verification, pruning, repair). TypeScript provides npm interface
via @push.rocks/smartrust RustBridge IPC with Unix socket streaming for ingest/restore.
All 14 integration tests pass.

rust/src/config.rs

@@ -0,0 +1,97 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct RepositoryConfig {
+    pub version: u32,
+    pub id: String,
+    pub created_at: String,
+    pub chunking: ChunkingConfig,
+    pub compression: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub encryption: Option<EncryptionConfig>,
+    pub pack_target_size: u64,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ChunkingConfig {
+    pub algorithm: String,
+    pub min_size: u32,
+    pub avg_size: u32,
+    pub max_size: u32,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct EncryptionConfig {
+    pub algorithm: String,
+    pub kdf: String,
+    pub kdf_params: KdfParams,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct KdfParams {
+    pub memory: u32,
+    pub iterations: u32,
+    pub parallelism: u32,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct KeyFile {
+    pub id: String,
+    pub created_at: String,
+    pub kdf: String,
+    pub kdf_salt: String,
+    pub kdf_params: KdfParams,
+    pub encrypted_key: String,
+    pub nonce: String,
+    pub auth_tag: String,
+}
+
+impl Default for ChunkingConfig {
+    fn default() -> Self {
+        Self {
+            algorithm: "fastcdc".to_string(),
+            min_size: 65536,      // 64 KB
+            avg_size: 262144,     // 256 KB
+            max_size: 1048576,    // 1 MB
+        }
+    }
+}
+
+impl Default for KdfParams {
+    fn default() -> Self {
+        Self {
+            memory: 262144,    // 256 MB
+            iterations: 3,
+            parallelism: 4,
+        }
+    }
+}
+
+impl Default for EncryptionConfig {
+    fn default() -> Self {
+        Self {
+            algorithm: "aes-256-gcm".to_string(),
+            kdf: "argon2id".to_string(),
+            kdf_params: KdfParams::default(),
+        }
+    }
+}
+
+impl RepositoryConfig {
+    pub fn new(encryption: Option<EncryptionConfig>) -> Self {
+        Self {
+            version: 1,
+            id: format!("repo-{}", uuid::Uuid::new_v4()),
+            created_at: chrono::Utc::now().to_rfc3339(),
+            chunking: ChunkingConfig::default(),
+            compression: "gzip".to_string(),
+            encryption,
+            pack_target_size: 8 * 1024 * 1024, // 8 MB
+        }
+    }
+}