fix(arch-updater): tighten package list UI and fix Dismiss/Update panel behavior (#289)

* fix(arch-updater): tighten package list spacing and icon size

* fix(arch-updater): make Dismiss actually clear the pending list

* fix(arch-updater): make hitting update close the panel

* feat(arch-updater): add per-source icons to the package list header

* feat(arch-updater): add an activity graph to the panel

Tracks the pending-update count across recent checks and when the last
update ran, persisted to disk so it survives restarts. Off also stops
recording history, not just hiding it.

* feat(arch-updater): show per-point detail on activity graph hover

ui.graph has no pointer props of its own, so a row of ghost buttons
sits under the line as per-point hit targets, each with a native
tooltip. History entries now carry a timestamp and whether the check
followed an update run, so hovering a point says when it happened and
either its pending count or "Updated".

* fix(arch-updater): load activity history at startup, not on first check

loadHistoryState() only ran lazily inside recordCheck/recordUpdateRun,
so a freshly started service published an empty history until a check
completed, hiding the graph even when prior sessions had data on disk.

* fix(arch-updater): render activity graph with sharp points, not curves

arch-updater/widget.luau

@@ -32,7 +32,6 @@ end
 local function pending()
     return snapshot ~= nil
         and snapshot.phase == "ready"
-        and snapshot.dismissed ~= true
         and (snapshot.total or 0) > 0
 end