fix(borgbackup): remove persistent timers to prevent post-resume failures

Removes persistentTimer from all borgbackup services and unnecessary
network-online.target dependencies. Changes fuchsia offsite to 14:00
fixed schedule when system is reliably awake.

Persistent timer catch-ups immediately after system resume caused
failures due to services starting before network/system fully stabilized:
- Onsite: DNS resolution failures (viridian.home.arpa)
- Offsite: BorgBase connection refusals during SSH/borg handshake

Fixed schedules provide reliable backups without catch-up complexity:
- fuchsia offsite: 14:00 daily (typical awake time for desktop)
- viridian offsite: midnight daily (always-on server)
- All onsite: hourly (no catch-up needed)

Offsite services retain wants/after dependencies on onsite completion
to prevent race conditions on shared /btrfs-subvolumes snapshot paths.

Network dependencies removed as fixed schedules run when system is
already stable, eliminating timing issues with network-online.target.

nixos/fuchsia/services/borgbackup/offsite.nix

@@ -82,11 +82,9 @@
     };
 
     environment.BORG_RSH = "ssh -i /etc/ssh/ssh_host_ed25519_key";
-    compression = "zstd,9";
-    startAt = "daily"; # Daily at midnight
 
-    # Ensure backup runs on next boot if system was asleep
-    persistentTimer = true;
+    compression = "zstd,9";
+    startAt = "14:00"; # Daily at 2pm when system is reliably awake
 
     # Retention policy for daily remote backups
     prune.keep = {

nixos/fuchsia/services/borgbackup/onsite.nix

@@ -13,8 +13,6 @@ in {
 
   # Configure service to wait for completion before marking as active
   systemd.services."borgbackup-job-onsite" = {
-    after = [ "network-online.target" ];
-    wants = [ "network-online.target" ];
     serviceConfig = {
       Type = "oneshot";
     };
@@ -82,9 +80,6 @@ in {
     compression = "zstd,9";
     startAt = "hourly";
 
-    # Ensure backup runs on wake if system was asleep
-    persistentTimer = true;
-
     # Match snapper retention policy
     prune.keep = {
       hourly = 24;

nixos/viridian/services/borgbackup/offsite.nix

@@ -104,9 +104,6 @@
     compression = "zstd,9";
     startAt = "daily"; # Daily at midnight
 
-    # Ensure backup runs on next boot if system was asleep
-    persistentTimer = true;
-
     # Retention policy for daily remote backups
     prune.keep = {
       daily = 7;      # Keep 7 daily backups (1 week)

nixos/viridian/services/borgbackup/onsite.nix

@@ -22,8 +22,6 @@ in {
 
   # Configure service to wait for completion before marking as active
   systemd.services."borgbackup-job-onsite" = {
-    after = [ "network-online.target" ];
-    wants = [ "network-online.target" ];
     serviceConfig = {
       Type = "oneshot";
     };
@@ -108,9 +106,6 @@ in {
     compression = "zstd,9";
     startAt = "hourly";
 
-    # Ensure backup runs on wake if system was asleep
-    persistentTimer = true;
-
     # Match snapper retention policy
     prune.keep = {
       hourly = 24;