Continue PR #142: security + Nix docs follow-up (#148)

* feat: add Nix Flake release and update documentation for Nix integration

- Added flake.nix with native library patching for Linux
- Included SHA256 hashes for v0.10.0 DEB releases (x86_64 and arm64)
- Updated README.md with instructions for nix run, NixOS, Home Manager, and devShells
- Generated flake.lock for reproducibility

* refactor: improve Nix Flake patterns for better consumer control

- Extracted derivation logic into a reusable `mkPackage` function
- Exposed `overlays.default` to allow consumers to use their own nixpkgs instance
- Updated `pkgs.system` to `pkgs.stdenv.hostPlatform.system` to follow modern Nix patterns
- Ensured default `packages` definition correctly handles unfree configuration for testing with `nix build` or `nix run`

* docs: update README with advanced Nix integration patterns

- Added Option 1 (Direct Integration) and Option 2 (Overlay) documentation
- Explained how to use the overlay for full nixpkgs control
- Fixed Markdown styling and lint issues in the Nix integration section

* docs: simplify Nix documentation to favor Overlay integration

- Removed "Option 1" (direct integration) as per user feedback
- Promoted the Overlay method as the standard way to consume the package
- Updated devShell examples to rely on the overlayed package set for consistency

* fix(security): prevent master key overwriting on decryption failure and improve account loading resilience

- Modify readSafeStorageKey and generatePrimaryMasterKey to stop if decryption fails for an existing file, preventing permanent data loss when keyring is temporarily locked.
- Update CloudAccountRepo.getAccounts and getAccount to gracefully skip corrupted account records instead of throwing errors.
- Added detailed logging for security failures to aid in diagnostics.

* docs(readme): sync Nix/NixOS integration docs in README.zh-CN

---------

Co-authored-by: Youssef <[email protected]>

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1774106199,
+        "narHash": "sha256-US5Tda2sKmjrg2lNHQL3jRQ6p96cgfWh3J1QBliQ8Ws=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "6c9a78c09ff4d6c21d0319114873508a6ec01655",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}