Theme Helix with the current Omarchy theme (#5530)

Helix had no theme integration. Installing it from the menu just ran
omarchy-pkg-add and left the editor on whatever default theme it shipped
with, regardless of the active Omarchy palette.

This adds `default/themed/helix.toml.tpl` so the template
renderer produces a helix.toml on every theme switch, and
`omarchy-install-helix` that wires Helix up:
  - install the package
  - symlink `~/.config/helix/themes/omarchy.toml` at the rendered theme
  - seed a config.toml selecting that theme when the user has none

The install menu routes Helix through this script. omarchy-restart-helix
joins omarchy-theme-set and signals Helix with SIGUSR1 so theme changes
are live [[1]], the same way as other packages. Arch-based distros
package the binary as 'helix' rather than upstream 'hx', so the new
scripts target 'helix' and the installer ends with a hint about aliasing
'hx'.

[1]: https://docs.helix-editor.com/configuration.html
Ref: https://github.com/basecamp/omarchy/discussions/4986

default/themed/helix.toml.tpl

@@ -0,0 +1,133 @@
+# Syntax
+"keyword" = "color5"
+"keyword.control" = { fg = "color5", modifiers = ["italic"] }
+"function" = "color4"
+"function.builtin" = "color4"
+"function.macro" = "color5"
+"type" = "color3"
+"type.builtin" = "color5"
+"type.enum.variant" = "color6"
+"constructor" = "color4"
+"constant" = "color3"
+"constant.builtin" = "color3"
+"constant.numeric" = "color3"
+"constant.character" = "color6"
+"constant.character.escape" = "color5"
+"string" = "color2"
+"string.regexp" = "color5"
+"string.special" = "color4"
+"comment" = { fg = "color8", modifiers = ["italic"] }
+"variable" = "foreground"
+"variable.parameter" = { fg = "color5", modifiers = ["italic"] }
+"variable.builtin" = "color1"
+"variable.other.member" = "color4"
+"label" = "color4"
+"punctuation" = "color8"
+"punctuation.special" = "color6"
+"operator" = "color6"
+"tag" = "color4"
+"namespace" = { fg = "color3", modifiers = ["italic"] }
+"special" = "color5"
+"attribute" = "color3"
+
+# Markup
+"markup.heading.1" = "color1"
+"markup.heading.2" = "color3"
+"markup.heading.3" = "color3"
+"markup.heading.4" = "color2"
+"markup.heading.5" = "color4"
+"markup.heading.6" = "color5"
+"markup.list" = "color6"
+"markup.list.unchecked" = "color8"
+"markup.list.checked" = "color2"
+"markup.bold" = { fg = "color1", modifiers = ["bold"] }
+"markup.italic" = { fg = "color1", modifiers = ["italic"] }
+"markup.strikethrough" = { modifiers = ["crossed_out"] }
+"markup.link.url" = { fg = "color4", modifiers = ["italic", "underlined"] }
+"markup.link.text" = "color5"
+"markup.link.label" = "color4"
+"markup.raw" = "color2"
+"markup.quote" = "color5"
+
+# Diff
+"diff.plus" = "color2"
+"diff.minus" = "color1"
+"diff.delta" = "color4"
+
+# Leave the editor background transparent so the terminal background shows through
+"ui.background" = { }
+
+"ui.linenr" = { fg = "color8" }
+"ui.linenr.selected" = { fg = "foreground" }
+
+# Statusline uses an inverted band (background-color text on foreground-color
+# background) to guarantee contrast across both light and dark Omarchy themes.
+"ui.statusline" = { fg = "background", bg = "foreground" }
+"ui.statusline.inactive" = { fg = "background", bg = "color8" }
+"ui.statusline.normal" = { fg = "background", bg = "color4", modifiers = ["bold"] }
+"ui.statusline.insert" = { fg = "background", bg = "color2", modifiers = ["bold"] }
+"ui.statusline.select" = { fg = "background", bg = "color5", modifiers = ["bold"] }
+
+"ui.popup" = { fg = "foreground", bg = "background" }
+"ui.window" = { fg = "color8" }
+"ui.help" = { fg = "foreground", bg = "background" }
+
+"ui.bufferline" = { fg = "color8", bg = "background" }
+"ui.bufferline.active" = { fg = "foreground", bg = "background", underline = { color = "color5", style = "line" } }
+
+"ui.text" = "foreground"
+"ui.text.focus" = { fg = "foreground", modifiers = ["bold"] }
+"ui.text.inactive" = { fg = "color8" }
+"ui.text.directory" = { fg = "color4" }
+
+"ui.virtual" = "color8"
+"ui.virtual.ruler" = { bg = "color0" }
+"ui.virtual.indent-guide" = "color8"
+"ui.virtual.inlay-hint" = { fg = "color8" }
+"ui.virtual.jump-label" = { fg = "color1", modifiers = ["bold"] }
+"ui.virtual.whitespace" = "color8"
+
+"ui.selection" = { fg = "selection_foreground", bg = "selection_background" }
+"ui.selection.primary" = { fg = "selection_foreground", bg = "selection_background" }
+
+"ui.cursor" = { fg = "background", bg = "cursor" }
+"ui.cursor.primary" = { fg = "background", bg = "cursor" }
+"ui.cursor.match" = { fg = "color3", modifiers = ["bold"] }
+"ui.cursor.primary.normal" = { fg = "background", bg = "cursor" }
+"ui.cursor.primary.insert" = { fg = "background", bg = "color2" }
+"ui.cursor.primary.select" = { fg = "background", bg = "color5" }
+
+"ui.cursorline.primary" = { bg = "color0" }
+
+"ui.highlight" = { fg = "selection_foreground", bg = "selection_background", modifiers = ["bold"] }
+
+"ui.menu" = { fg = "foreground", bg = "background" }
+"ui.menu.selected" = { fg = "background", bg = "foreground", modifiers = ["bold"] }
+
+"diagnostic.error" = { underline = { color = "color1", style = "curl" } }
+"diagnostic.warning" = { underline = { color = "color3", style = "curl" } }
+"diagnostic.info" = { underline = { color = "color4", style = "curl" } }
+"diagnostic.hint" = { underline = { color = "color6", style = "curl" } }
+"diagnostic.unnecessary" = { modifiers = ["dim"] }
+"diagnostic.deprecated" = { modifiers = ["crossed_out"] }
+
+error = "color1"
+warning = "color3"
+info = "color4"
+hint = "color6"
+
+[palette]
+background = "{{ background }}"
+foreground = "{{ foreground }}"
+cursor = "{{ cursor }}"
+selection_background = "{{ selection_background }}"
+selection_foreground = "{{ selection_foreground }}"
+color0 = "{{ color0 }}"
+color1 = "{{ color1 }}"
+color2 = "{{ color2 }}"
+color3 = "{{ color3 }}"
+color4 = "{{ color4 }}"
+color5 = "{{ color5 }}"
+color6 = "{{ color6 }}"
+color7 = "{{ color7 }}"
+color8 = "{{ color8 }}"