feat: add power gauge/delta/minmax to ac-power and extract shared utils

ac-power enhancements:
- Add visual block gauge [████░░░░] colored by power level
- Show delta indicator (+50W) colored by trend (green=dropping, red=rising)
- Track min/max values with persistence to ~/.cache/mpv/
- Multi-process safe file writes (merges values on save)
- New script-message: ac-power-reset-minmax

Shared library (scripts/lib/utils.lua):
- Extract common helpers: trim, clamp, rgb_to_bgr, colorize
- Update all scripts to use shared module via package.path

scripts/touch-gestures.lua

@@ -50,6 +50,9 @@ local mp = require("mp")
 local msg = require("mp.msg")
 local utils = require("mp.utils")
 
+package.path = mp.command_native({ "expand-path", "~~/scripts/lib/?.lua;" }) .. package.path
+local lib = require("utils")
+
 local state = {
   active = false,
   zone = nil,
@@ -72,16 +75,6 @@ local function dbg(text)
   end
 end
 
-local function clamp(value, min_v, max_v)
-  if value < min_v then
-    return min_v
-  end
-  if value > max_v then
-    return max_v
-  end
-  return value
-end
-
 local function run_cmd(args)
   local res = utils.subprocess({ args = args, cancellable = false })
   if not res or res.error or res.status ~= 0 then
@@ -149,7 +142,7 @@ local function current_brightness_percent()
     local cur, max = out:match(",(%d+),(%d+),")
     local c, m = tonumber(cur), tonumber(max)
     if c and m and m > 0 then
-      state.cached_brightness_pct = clamp((c / m) * 100, 0, 100)
+      state.cached_brightness_pct = lib.clamp((c / m) * 100, 0, 100)
       return state.cached_brightness_pct
     end
   end
@@ -163,12 +156,12 @@ local function current_brightness_percent()
   if not c or not m or m <= 0 then
     return nil
   end
-  state.cached_brightness_pct = clamp((c / m) * 100, 0, 100)
+  state.cached_brightness_pct = lib.clamp((c / m) * 100, 0, 100)
   return state.cached_brightness_pct
 end
 
 local function set_brightness_percent(pct)
-  local target = clamp(pct, config.min_brightness, 100)
+  local target = lib.clamp(pct, config.min_brightness, 100)
   local ok = run_cmd(brightness_args({ "set", string.format("%.2f%%", target) }))
   if ok then
     state.cached_brightness_pct = target
@@ -191,7 +184,7 @@ local function current_volume_percent()
     if not val then
       return nil
     end
-    state.cached_volume_pct = clamp(val * 100, 0, config.max_volume)
+    state.cached_volume_pct = lib.clamp(val * 100, 0, config.max_volume)
     return state.cached_volume_pct
   elseif backend == "pactl" then
     local out = run_cmd({ config.pactl_path, "get-sink-volume", "@DEFAULT_SINK@" })
@@ -203,7 +196,7 @@ local function current_volume_percent()
     if not pct then
       return nil
     end
-    state.cached_volume_pct = clamp(pct, 0, config.max_volume)
+    state.cached_volume_pct = lib.clamp(pct, 0, config.max_volume)
     return state.cached_volume_pct
   end
   return nil
@@ -214,7 +207,7 @@ local function set_volume_percent(pct)
   if not backend then
     return
   end
-  local target = clamp(pct, 0, config.max_volume)
+  local target = lib.clamp(pct, 0, config.max_volume)
   if backend == "wpctl" then
     run_cmd({
       config.wpctl_path,