fix: FQDN resolution and display_name blank bug; fix: Arch/Alpine/RPM packages

Bug fixes:
- get_fqdn() now prioritizes 'hostname -f' (returns full FQDN) over /etc/hostname (returns short hostname)
- Added get_hostname() for short hostname extraction
- Added hostname field to EnrollmentRequest for manager display_name population
- Updated SPEC.md and API_DOCUMENTATION.md

Package fixes:
- Arch: Added linux-patch-api.install with post_install/upgrade/remove hooks, user creation, directory creation, config handling
- Alpine: Added linux-patch-api.apk-install with pre/post install/deinstall hooks, user creation, directory creation, config handling, missing config.yaml.example
- RPM: Dynamic version from Cargo.toml, %ghost %config(noreplace) for live configs, tarball exclusions, /var/log in %files

SPEC.md

@@ -169,7 +169,7 @@ The enrollment flow runs before mTLS server startup. On success, the daemon proc
 ### Phase 1: Registration Request
 - **Identity Extraction:**
   - `/etc/machine-id` (fallback: `/var/lib/dbus/machine-id`)
-  - FQDN from `/etc/hostname` → `hostname -f` → `hostname` → `localhost`
+  - FQDN from `hostname -f` (validated contains `.`) → `hostname` + `hostname -d` → `/etc/hostname` → `hostname` → `localhost`
   - Non-loopback IPv4 addresses via network interface enumeration
   - OS details from `/etc/os-release` (distro, version, id_like, codename) + kernel version (`uname -r`)
 - **Submission:** Unauthenticated `POST /api/v1/enroll` to manager with identity payload