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.

.gitignore

@@ -0,0 +1,28 @@
+.nogit/
+
+# artifacts
+coverage/
+public/
+pages/
+
+# installs
+node_modules/
+
+# caches
+.yarn/
+.cache/
+.rpt2_cache
+
+# builds
+dist/
+dist_*/
+
+# AI
+.claude/
+.serena/
+
+# Rust
+rust/target/
+
+#------# custom
+.playwright-mcp/