Add procmon plugin with live process panel (#301)

* Add procmon plugin with live process panel

New Noctalia plugin: bar widget shows CPU/RAM usage and process
count; floating panel has a sortable, searchable process table
with per-process kill. Background service samples ps and /proc
stats and publishes via plugin state.

* Throttle data-driven panel renders

Rebuild table at most every 500ms to stay within the panel update
CPU budget. User interactions still render immediately; only state
watches and the tick go through maybeRender().

* Update procmon deps and fix timestamp precision

Document head, grep, and cat as required commands. Correct refresh
interval default to 1000 ms. Sample refreshedAtMs in milliseconds.

procmon/widget.luau

@@ -0,0 +1,56 @@
+--!nonstrict
+-- Process Monitor — bar widget. Full mode shows "CPU% RAM% · count" text; icon-only
+-- mode shows just a CPU icon colored by load, with the details in the tooltip so the
+-- bar stays tiny. Clicking opens the panel.
+
+local function cfg(key)
+	return noctalia.getConfig(key)
+end
+
+local function st(key)
+	return noctalia.state.get(key)
+end
+
+local function tr(key, subst)
+	return noctalia.tr(key, subst)
+end
+
+function update()
+	local stats = st("stats")
+	local cpu = stats and stats.cpu and stats.cpu.usagePercent
+	local ram = stats and stats.ram and stats.ram.usagePercent
+	local count = #(st("procs") or {})
+	local cpuInt = math.floor(cpu or 0)
+	local tooltip = tr("widget.tooltip", { cpu = cpuInt, ram = math.floor(ram or 0), n = count })
+
+	barWidget.setGlyph(cfg("glyph") or "cpu")
+	barWidget.setTooltip(tooltip)
+
+	if cfg("icon_only") then
+		barWidget.setText("")
+		-- color the icon by CPU load so a glance reads the machine state
+		if cpuInt >= 80 then
+			barWidget.setGlyphColor("error")
+		elseif cpuInt >= 50 then
+			barWidget.setGlyphColor("warning")
+		else
+			barWidget.setGlyphColor("on_surface")
+		end
+		return
+	end
+
+	barWidget.setGlyphColor("on_surface")
+	local text = string.format("CPU %d%%  RAM %d%%", cpuInt, math.floor(ram or 0))
+	if cfg("show_count") then
+		text = text .. "  ·  " .. count
+	end
+	barWidget.setText(text)
+end
+
+noctalia.state.watch("stats", update)
+noctalia.state.watch("procs", update)
+noctalia.setUpdateInterval(1000)
+
+function onClick()
+	noctalia.togglePanel("weinguyen/procmon:panel")
+end