refactor: update dependencies and remove unused code

- Added new dependencies: `adler2`, `crc32fast`, `flate2`, `miniz_oxide`, and `libredox`.
- Updated existing dependencies: `tokio-rustls` to version 0.26.4 and `filetime` to version 0.2.27.
- Removed the `backup.rs` file as it is no longer needed.
- Introduced tests for configuration and credential management.
- Enhanced the `identity` module to generate W3C compliant DID documents.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/arm64-build.md

@@ -0,0 +1,114 @@
+# ARM64 (aarch64) Cross-Compilation Guide
+
+## Overview
+
+Archipelago supports both x86_64 and ARM64 (aarch64) platforms. The backend is compiled natively on x86_64 and cross-compiled for ARM64 targets like Raspberry Pi 5.
+
+## Prerequisites
+
+### On the Build Server (Debian 12)
+
+```bash
+# 1. Add the ARM64 Rust target
+rustup target add aarch64-unknown-linux-gnu
+
+# 2. Install the cross-linker and C library
+sudo apt update
+sudo apt install -y gcc-aarch64-linux-gnu libc6-dev-arm64-cross
+
+# 3. Install cross-compilation OpenSSL headers (for reqwest/hyper TLS)
+sudo apt install -y libssl-dev:arm64
+# If the above fails (no multiarch), use vendored OpenSSL instead:
+# Set OPENSSL_STATIC=1 and add openssl = { version = "0.10", features = ["vendored"] }
+```
+
+### Cargo Configuration
+
+The cross-compilation config is at `core/.cargo/config.toml`:
+
+```toml
+[target.aarch64-unknown-linux-gnu]
+linker = "aarch64-linux-gnu-gcc"
+```
+
+## Building
+
+### Native (x86_64)
+
+```bash
+cd core
+cargo build --release -p archipelago
+# Output: core/target/release/archipelago
+```
+
+### ARM64 Cross-Compilation
+
+```bash
+cd core
+
+# Option A: System OpenSSL (requires libssl-dev:arm64)
+PKG_CONFIG_ALLOW_CROSS=1 \
+PKG_CONFIG_PATH=/usr/lib/aarch64-linux-gnu/pkgconfig \
+cargo build --release --target aarch64-unknown-linux-gnu -p archipelago
+
+# Output: core/target/aarch64-unknown-linux-gnu/release/archipelago
+
+# Option B: Vendored OpenSSL (no system packages needed)
+OPENSSL_STATIC=1 \
+cargo build --release --target aarch64-unknown-linux-gnu -p archipelago
+```
+
+### Verify the Binary
+
+```bash
+file core/target/aarch64-unknown-linux-gnu/release/archipelago
+# Should show: ELF 64-bit LSB pie executable, ARM aarch64, ...
+```
+
+## Using `cross` (Alternative)
+
+The `cross` tool uses Docker containers for hermetic cross-compilation:
+
+```bash
+cargo install cross
+
+# Build for ARM64 (downloads a Docker image with all dependencies)
+cross build --release --target aarch64-unknown-linux-gnu -p archipelago
+```
+
+This is the simplest approach and avoids installing system cross-compilation packages.
+
+## Troubleshooting
+
+### `cannot find -lssl` / `cannot find -lcrypto`
+
+OpenSSL headers for ARM64 are missing. Either:
+- Install `libssl-dev:arm64` (requires multiarch support)
+- Use vendored OpenSSL: set `OPENSSL_STATIC=1`
+- Add `openssl = { version = "0.10", features = ["vendored"] }` to Cargo.toml
+
+### `cc: error: unrecognized command-line option`
+
+The wrong linker is being used. Verify `aarch64-linux-gnu-gcc` is installed:
+```bash
+which aarch64-linux-gnu-gcc
+aarch64-linux-gnu-gcc --version
+```
+
+### `Exec format error` when running
+
+You're trying to run an ARM64 binary on x86_64. Use `qemu-aarch64-static` for testing:
+```bash
+sudo apt install qemu-user-static
+qemu-aarch64-static ./archipelago
+```
+
+## Target Hardware
+
+| Device | Arch | Status |
+|--------|------|--------|
+| Raspberry Pi 5 | aarch64 | Primary ARM target |
+| Raspberry Pi 4 | aarch64 | Supported |
+| Rock Pi 4 | aarch64 | Untested |
+| Orange Pi 5 | aarch64 | Untested |
+| x86_64 NUC/Mini PC | x86_64 | Primary platform |