feat(snapshots): desktop browse/restore + snapshot /home by default

Surface snapper snapshots from the desktop: `nomarchy-menu snapshot` (in the
SUPER+M picker, self-gated) launches btrfs-assistant, the polkit-aware
browse/diff/restore/rollback UI -- safer than a fat-fingerable rofi rollback
for a destructive root-only op. Shipped system-side gated on
nomarchy.system.snapper.

Also snapshot /home by default (hourly 5 / daily 7 / weekly 4) when it's its
own BTRFS subvolume -- the installer only set up snapper for /. A boot
oneshot creates the required /home/.snapshots subvolume if missing, so
already-installed machines get it too (no disko change).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -295,10 +295,16 @@ how to override it. Items marked ✓ are shipped.
   right-click toggles DND). Turning DND off confirms with a toast; turning
   it on is silent (notifications are suppressed — the bell-off glyph is the
   cue).
-- **Snapshot browse/restore UX:** snapper already takes BTRFS timeline
-  snapshots (`nomarchy.system.snapper`); surface them from the desktop — a
-  rofi menu (or btrfs-assistant) to browse/diff/restore and boot-from-
-  snapshot — so rollback isn't CLI-only.
+- ✓ **Snapshot browse/restore UX:** `nomarchy-menu snapshot` (in the SUPER+M
+  picker, self-gated on snapper) launches **btrfs-assistant** — the
+  desktop browse/diff/restore/rollback UI, elevating via polkit (the safe
+  choice for a destructive, root-only op vs a fat-fingerable rofi rollback).
+  Shipped system-side gated on `nomarchy.system.snapper`. Also extended
+  snapper to snapshot **/home** by default (hourly 5 / daily 7 / weekly 4)
+  when it's its own BTRFS subvolume; a boot oneshot creates the required
+  `/home/.snapshots` subvolume if missing (covers existing installs, no disko
+  change). Remaining (optional): a keyboard-driven rofi browse for quick
+  glances; boot-from-snapshot needs a systemd-boot equivalent of grub-btrfs.
 - **Update awareness:** updates are manual today (`sys-update`/`home-update`);
   add a Waybar indicator / notification when flake inputs are stale or a new
   nixpkgs rev is available (optionally with a pending-change count). Augments,