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/playback-health.lua

@@ -48,6 +48,9 @@ local config = {
 local mp = require("mp")
 local msg = require("mp.msg")
 
+package.path = mp.command_native({ "expand-path", "~~/scripts/lib/?.lua;" }) .. package.path
+local lib = require("utils")
+
 local state = {
   is_stream = false,
   buffering = false,
@@ -69,21 +72,6 @@ local function dbg(text)
   end
 end
 
-local function rgb_to_bgr(rgb)
-  local r = rgb:sub(1, 2)
-  local g = rgb:sub(3, 4)
-  local b = rgb:sub(5, 6)
-  return b .. g .. r
-end
-
-local function colorize(text, color_rgb)
-  if not config.use_colors then
-    return text
-  end
-  local bgr = rgb_to_bgr(color_rgb)
-  return "{\\1c&H" .. bgr .. "&}" .. text .. "{\\1c&HFFFFFF&}"
-end
-
 local function clear_osd()
   mp.set_osd_ass(0, 0, "")
 end
@@ -189,14 +177,14 @@ local function show_warning(warning_type, message, color)
   state.last_warning[warning_type] = mp.get_time()
   state.active_warning = warning_type
   local col = color or config.color_warning
-  local styled = colorize("⚠ " .. message, col)
+  local styled = lib.colorize("⚠ " .. message, col, config.use_colors)
   show_osd(styled, config.osd_duration)
   dbg(("warning: %s"):format(message))
 end
 
 local function show_recovery()
   if state.active_warning and config.show_recovery then
-    local styled = colorize("✓ Recovered", config.color_recovery)
+    local styled = lib.colorize("✓ Recovered", config.color_recovery, config.use_colors)
     show_osd(styled, config.osd_duration)
     dbg("recovery shown")
   end
@@ -256,12 +244,13 @@ local function on_cache_buffering_state(_, pct)
       local eta = predict_buffer_time(cache, target)
       local eta_str = format_prediction(eta)
       if eta_str then
-        local pred = colorize("(" .. eta_str .. " to resume)", config.color_info)
+        local pred =
+          lib.colorize("(" .. eta_str .. " to resume)", config.color_info, config.use_colors)
         table.insert(parts, pred)
       end
     end
     local text = table.concat(parts, " ")
-    local styled = colorize("⚠ " .. text, config.color_warning)
+    local styled = lib.colorize("⚠ " .. text, config.color_warning, config.use_colors)
     show_osd(styled, config.osd_duration)
   end
 end
@@ -294,7 +283,8 @@ local function on_cache_duration(_, duration)
       local eta = predict_buffer_time(duration, 0)
       local eta_str = format_prediction(eta)
       if eta_str then
-        local pred = colorize("(stall in " .. eta_str .. ")", config.color_info)
+        local pred =
+          lib.colorize("(stall in " .. eta_str .. ")", config.color_info, config.use_colors)
         table.insert(parts, pred)
       end
     end