Adopt mods dropped beside the game instead of ignoring them

love.filesystem looks for "mods/" in two places: the save directory, and
-- portable installs only -- the game folder, which CacheFs mounts. So a
player who unzips a mod next to the executable of an ordinary install,
which is where very nearly every other game would want it, gets no error
and no mod. The panel just comes up empty, with nothing on screen to
suggest the files are sitting in the wrong folder twenty centimetres away.

That is a hard failure to self-diagnose, and it is worse behind a
launcher: the install lives somewhere the player never opens, so "the
game's mods folder" is a guess to begin with.

The mods panel now looks in those folders before its first listing and
copies what it finds into the tree the game really reads, reporting what
it took in the notice line. It happens on open rather than behind a
button because the failure being fixed is one where nothing suggests
there is anything to press.

Looking is scoped: CacheFs.withMounted puts the folder on the read path
at its own mount point, runs the scan, and takes it straight back off.
Nothing a stray folder contains can shadow a game file or change what the
running game resolves, which is what makes it safe to point at a folder
whose contents nobody has validated. Adoption skips ids the game can
already see, so it is idempotent and never nags twice, and it leaves the
loose folder alone -- deleting files outside the save directory on the
player's behalf is not this code's call to make.

Which strays are worth taking is pure (LauncherMods.pickStrays), matching
how deriveList and locateRoot are already split out, so the engine tier
covers the rules without needing love. SaveData.gameFolders is the old
detectPortable candidate list lifted out unchanged -- portable mode is
just the case where one of those folders holds the marker.

Claude-Session: https://claude.ai/code/session_01JvEthuoNBPfxpvHUD9Pd4N

src/import/RomImporter.lua

@@ -2697,6 +2697,30 @@ end
 -- so a still list costs nothing after the first paint.
 function RomImporter:_refreshMods()
   local LauncherMods = require("src.mods.LauncherMods")
+  -- Once per session, ahead of the first listing: pull in any mod the player
+  -- unzipped beside the executable, which an ordinary (non-portable) install
+  -- has no way to read.  It happens here rather than behind a button because
+  -- the failure being fixed is one where nothing on screen suggests there is
+  -- anything to press -- the panel just comes up empty.  Guarded so a toggle
+  -- or a delete does not re-scan; adoptStrays is idempotent regardless.
+  if not self.modStraysChecked then
+    self.modStraysChecked = true
+    local imported, failed = {}, {}
+    for _, s in ipairs(LauncherMods.adoptStrays() or {}) do
+      table.insert(s.err and failed or imported, s.id)
+    end
+    -- the failure wins the notice: an import that worked speaks for itself in
+    -- the list right below it, one that did not is the only word they get
+    if #imported > 0 then
+      self.modNotice = { ok = true,
+        text = "Imported from the game folder: " .. table.concat(imported, ", ") }
+    end
+    if #failed > 0 then
+      self.modNotice = { ok = false,
+        text = "Found beside the game but could not import: "
+               .. table.concat(failed, ", ") }
+    end
+  end
   self.mods = LauncherMods.list() or {}
 end