chore(pack): mark Distant Horizons as an optional mod

Adds an [option] block so Distant Horizons is a user-toggleable mod instead
of always installed, matching how Controlify is already declared.

default = false expresses opt-in wherever the consuming exporter supports
it: modrinth/export.go reads only Optional, so in an mrpack the mod becomes
a toggle (that format has no off-by-default concept), while
curseforge/export.go reads Default and marks it optional-and-disabled.

Nothing in the pack depends on or conflicts with Distant Horizons, so no
other mod is left unsatisfied by it being skippable.

pack.toml

@@ -6,7 +6,7 @@ pack-format = "packwiz:1.1.0"
 [index]
 file = "index.toml"
 hash-format = "sha256"
-hash = "b39ae3e18dd3f48977aee61c3bd1c9b2693facfa7aaab341e2bb1086b78a15a3"
+hash = "7d758d2aeb2da1f75c664ca98d55490febfede6c7dcd3db277595134350de168"
 
 [versions]
 minecraft = "1.21.1"