Make displays configurable, with a revert countdown

Resolution, refresh rate, scale, and rotation, applied through
hl.monitor{} and stored per output.

This is the only setting in Panama where a wrong value can leave the
user unable to SEE the screen well enough to undo it: a mode the panel
cannot show, or a scale that makes everything unreadable, is not
recoverable through the UI that caused it. So a change is never applied
irreversibly. It is applied, then reverted automatically after fifteen
seconds unless confirmed, and confirming is what writes it to the
settings store -- letting the countdown run leaves nothing behind.

The contract tests that property specifically: it applies a scale, waits
out the countdown, and asserts the display came back and that nothing
was stored. A regression there is not a broken feature, it is a user
staring at a blank monitor.

Modes are grouped by resolution with refresh rates beside them. The
panel reports 35, many differing only in refresh-rate rounding -- 60.00
and 59.94 -- which as a flat list of buttons is noise rather than
choice; equal rounded pairs collapse, leaving 21.

Only mode, scale, and transform are configurable. Colour management and
bit depth stay in monitors.lua because they carry a documented screencopy
tradeoff that a settings page cannot explain at the moment you would be
changing it.

Also replaces the display policy rows with the schema-bound ones, so the
page no longer restates labels that PreferenceSchema already holds.

Claude-Session: https://claude.ai/code/session_01BRvzt4H8XXLPVH5MyYdk9L

config/dot/hypr/monitors.lua

@@ -17,11 +17,35 @@
 -- overrides.lua) and read the notes in that file first.
 -- ─────────────────────────────────────────────────────────────────────────────
 
+local prefs = require("prefs")
+
+-- Per-output overrides written by Panama Settings, keyed by output name:
+--   { ["DP-2"] = { mode = "3840x2160@60", scale = 2, transform = 0 } }
+--
+-- Only mode, scale, and transform are read. Colour management and bit depth
+-- stay here, because those are the settings with a documented reason attached
+-- (see the header) rather than preferences, and a settings page has no way to
+-- explain the screencopy tradeoff at the moment you would be changing it.
+local displays = prefs.get("displays", {})
+
+local function override(output, field, fallback)
+    local entry = displays[output]
+    if type(entry) ~= "table" then
+        return fallback
+    end
+    local value = entry[field]
+    if value == nil or type(value) ~= type(fallback) then
+        return fallback
+    end
+    return value
+end
+
 hl.monitor({
     output   = "DP-2",
-    mode     = "4500x3000@60",
+    mode     = override("DP-2", "mode", "4500x3000@60"),
     position = "0x0",
-    scale    = 1.5,
+    scale    = override("DP-2", "scale", 1.5),
+    transform = override("DP-2", "transform", 0),
 
     -- 10-bit output. 4500x3000@60 at 10bpc is ~24 Gbps, right at the edge of
     -- DP 1.4 HBR3, so this relies on DSC. If the display fails to light up or