ghostty: restore faithful australis port

The tracked theme had drifted from the palette source. Cursor and
selection values did not match wezterm/config.lua in the australis
repo, which the port is derived from:

  cursor-color         #51e08a -> #6388d8  (wezterm cursor_bg)
  cursor-text          absent  -> #373b46  (wezterm cursor_fg)
  selection-foreground #cce7ec -> #373b46  (wezterm selection_fg)

Neither #51e08a nor #cce7ec appears in the wezterm cursor or
selection configuration. All sixteen palette entries were already
correct and are unchanged; the drift was confined to cursor and
selection. Also restores the header comment citing the upstream
source.

home_config/ghostty/themes/australis

@@ -1,37 +1,32 @@
+# Australis (Aurora Australis) — dark theme
+# Ported to Ghostty from the WezTerm config at
+# https://github.com/vh-pfi/australis  (wezterm/config.lua)
+
 background = #222531
 foreground = #a9bcc3
-cursor-color = #51e08a
+
+cursor-color = #6388d8
+cursor-text  = #373b46
+
 selection-background = #6388d8
-selection-foreground = #cce7ec
+selection-foreground = #373b46
 
-# Black / Bright Black
+# Normal (ANSI 0-7)
 palette = 0=#222531
-palette = 8=#373b46
-
-# Red / Bright Red
 palette = 1=#ff491a
-palette = 9=#ff854f
-
-# Green / Bright Green
 palette = 2=#16b866
-palette = 10=#51e08a
-
-# Yellow / Bright Yellow
 palette = 3=#e1c631
-palette = 11=#ffe14e
-
-# Blue / Bright Blue
 palette = 4=#6388d8
-palette = 12=#a4c4ff
-
-# Magenta / Bright Magenta
 palette = 5=#9d78ff
-palette = 13=#d8adff
-
-# Cyan / Bright Cyan
 palette = 6=#00b1a8
-palette = 14=#42dcd1
-
-# White / Bright White
 palette = 7=#a9bcc3
+
+# Bright (ANSI 8-15)
+palette = 8=#373b46
+palette = 9=#ff854f
+palette = 10=#51e08a
+palette = 11=#ffe14e
+palette = 12=#a4c4ff
+palette = 13=#d8adff
+palette = 14=#42dcd1
 palette = 15=#cce7ec