fix(nix): ensure absolute bundle path in pre-sync backup (#204)

* fix(nix): ensure absolute bundle path in pre-sync backup (#203)

Use path.resolve() instead of conditional path.isAbsolute() check to
guarantee bundlePath is always absolute before passing to git -C. On
NixOS, relative paths were interpreted relative to the temp mirror
clone directory, causing "No such file or directory" errors.

Closes #203

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

* fix(nix): ensure absolute bundle path in pre-sync backup (#203)

Use path.resolve() instead of conditional path.isAbsolute() check to
guarantee bundlePath is always absolute before passing to git -C. On
NixOS, relative paths were interpreted relative to the temp mirror
clone directory, causing "No such file or directory" errors.

Extract resolveBackupPaths() for testability. Bump version to 3.10.1.

Closes #203

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

* ci: drop macos matrix and only run nix build on main/tags

- Remove macos-latest from Nix CI matrix (ubuntu-only)
- Only run `nix build` on main branch and version tags, skip on PRs
- `nix flake check` still runs on all PRs for validation

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "gitea-mirror",
   "type": "module",
-  "version": "3.10.0",
+  "version": "3.10.1",
   "engines": {
     "bun": ">=1.2.9"
   },