Fix lingering title music after Resume Game

Continue dropped the player into the overworld with the title
screen's song still cross-fading into the map theme over ~1.2s
(Music.MAP_FADE), audibly wrong since the player already has control.
New Game never showed this because OakSpeech's own unfaded
Music.play/playMap masks it before the player is ever placed in the
overworld. The same bug was also reachable through F2 quickload
(pressed at the title screen, or mid-session -- F2 always jumps
straight to the loaded save's map/position with no walking
transition, so it needs the same instant swap as Continue rather than
an ordinary warp's crossfade either way) and through the
checkpoint-resume mod API (RFC 0006's mod.checkpoint:resume).

OverworldState:setMap now takes an opts.freshBoot flag: when set, the
map's music swaps in at once instead of cross-fading, like every
other map's PlayDefaultMusic. It is set by every real hard state
teleport -- TitleState's onContinue, New Game's push, F2 quickload,
and Game:restoreCheckpointSave (whose only caller is itself
title-gated) -- and deliberately kept separate from the pre-existing
opts.via == "boot" default, which dev tooling (the console's `warp`
verb, hot reload's map rebuild) also reuses for unrelated reasons and
must keep its ordinary crossfade.

src/world/OverworldController.lua

@@ -462,8 +462,18 @@ function OverworldState:setMap(mapId, x, y, facing, opts)
   if not keepMusic then
     -- ..(home/overworld.asm ln 2346)
     local Music = require("src.core.Music")
+    -- opts.freshBoot: switch instantly instead of cross-fading, like every
+    -- other map's PlayDefaultMusic on real hardware -- set only by
+    -- Game.lua's hard state teleports (onContinue, New Game, F2,
+    -- restoreCheckpointSave). Deliberately separate from opts.via ==
+    -- "boot" itself: dev tooling (src/dev/Console.lua's warp verb,
+    -- src/dev/HotReload.lua's reloadMap) reuses that same default for the
+    -- surf-restore/fresh-npc-pool branches above and must keep the
+    -- ordinary crossfade.
+    local fade = Music.MAP_FADE
+    if opts and opts.freshBoot then fade = nil end
     Music.playMap(Game.data, mapId, Game.save.onBike, self.player.surfing,
-                  Music.MAP_FADE)
+                  fade)
   end
 
   -- forced bike/surf tiles fire the moment the player is placed on the