fix(theme): keep the live mode and Dreamcoder colours stable across mode switches

[Dreamcoder08]

Summary

A bare dreamcoder sync rendered Dark over a Light system, ML4W's GTK listener re-ran Matugen over Dreamcoder colours on every switch, and a few apply steps hung or were silently undone.

Changes

• theme_mode() falls back to the persisted live mode before defaulting to dark; fish starts in that mode
• Marked hook in ML4W's gtk-theme-switcher.sh that re-applies Dreamcoder colours right after each Matugen run
• restart_waybar detaches the relaunched bar from the caller's streams (theme apply no longer hangs)
• btop color_theme re-selected on every apply
• ls colours for broken links and sticky dirs lifted to WCAG AA, with a 4.5:1 gate test

Verification

New tests for each behaviour (mode resolution, listener fixture copied from ML4W 2.16, waybar detach, contrast gate); full suites green; a real dark to light toggle on a live machine leaves Starship, Hyprland and Waybar in Light.

Chain Context

Field	Value
Chain	ML4W 2.16 + Herdr 0.9.1 + Light/Dark-only stabilisation
Tracker PR	Not needed (stacked PRs to main)
Position	3 of 6
Base	pr/02-stow-herdr-0.9.1
Depends on	#12
Follow-up	#14
Review budget	669 / 400
Starts at	the tip of pr/02-stow-herdr-0.9.1
Ends with	fix(theme): keep the live mode and Dreamcoder colours stable across mode switches

Chain Overview

main
 └── #11 fix(ml4w)
  └── #12 fix(install)
   └── 📍 #13 fix(theme)
    └── #14 fix(shell)
     └── #15 refactor(theme)
      └── #16 chore(quality)

Scope

• Includes: see Changes above
• Excludes:
• Shell option safety (PR 4)

Autonomy

• CI is expected to pass for this PR branch
• This PR has one deliverable scope
• This PR can be rolled back without unrelated changes
• Tests, docs, or manual verification cover this unit

[Dreamcoder08]

Verified independently at this slice tip (stacked PRs do not run CI until retargeted to main): pytest exit 0, ruff clean, bats 1 failure. The single bats failure is apply-theme-mode.sh kanagawa bridge carries night-derived colors, which already fails on main; it is removed together with Night in #15 (bats 0 failures there).