Fix Ayu Dark/Mirage dim terminal colors appearing as white (#51462)

## Summary

Closes #46126

Dim terminal colors in **Ayu Dark** and **Ayu Mirage** were defined as
light pastels instead of muted/darker versions of the normal colors. On
a dark background, the APCA minimum contrast algorithm boosted these
already-light colors toward white, making "dimmed" text (e.g.
zsh-autosuggestions) appear brighter than normal text.

### Root cause

| Color | Ayu Dark (before) | Ayu Dark (after) | Pattern |
|-------|-------------------|------------------|---------|
| dim_foreground | `#0d1016` (= background!) | `#85847f` | Muted
foreground |
| dim_red | `#febab9` (light pink) | `#a74f53` | 70% of normal red |
| dim_green | `#d8eca8` (light pastel) | `#769735` | 70% of normal green
|
| dim_yellow | `#ffd9aa` (light pastel) | `#b17d3a` | 70% of normal
yellow |

The fix follows the same convention as **Gruvbox** and **One Dark**,
where dim = ~70% brightness of the normal color.

**Ayu Light** was already correct (dim colors are darker, which is
correct for light backgrounds).

## Test plan

- [ ] Open terminal in Zed with Ayu Dark theme
- [ ] Enable zsh-autosuggestions (or any tool that uses dim/faint ANSI
colors)
- [ ] Type a partial command to trigger autosuggestions
- [ ] Verify suggested text appears as muted/dim, not bright white
- [ ] Repeat with Ayu Mirage theme
- [ ] Verify Ayu Light theme is unaffected

---

Release Notes:

- Improved some Ayu Dark/Mirage theme's terminal colors.

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

assets/themes/ayu/ayu.json

@@ -71,31 +71,31 @@
         "terminal.background": "#0d1016ff",
         "terminal.foreground": "#bfbdb6ff",
         "terminal.bright_foreground": "#bfbdb6ff",
-        "terminal.dim_foreground": "#0d1016ff",
+        "terminal.dim_foreground": "#85847fff",
         "terminal.ansi.black": "#0d1016ff",
         "terminal.ansi.bright_black": "#545557ff",
-        "terminal.ansi.dim_black": "#bfbdb6ff",
+        "terminal.ansi.dim_black": "#3a3b3cff",
         "terminal.ansi.red": "#ef7177ff",
         "terminal.ansi.bright_red": "#83353bff",
-        "terminal.ansi.dim_red": "#febab9ff",
+        "terminal.ansi.dim_red": "#a74f53ff",
         "terminal.ansi.green": "#aad84cff",
         "terminal.ansi.bright_green": "#567627ff",
-        "terminal.ansi.dim_green": "#d8eca8ff",
+        "terminal.ansi.dim_green": "#769735ff",
         "terminal.ansi.yellow": "#feb454ff",
         "terminal.ansi.bright_yellow": "#92582bff",
-        "terminal.ansi.dim_yellow": "#ffd9aaff",
+        "terminal.ansi.dim_yellow": "#b17d3aff",
         "terminal.ansi.blue": "#5ac1feff",
         "terminal.ansi.bright_blue": "#27618cff",
-        "terminal.ansi.dim_blue": "#b7dffeff",
+        "terminal.ansi.dim_blue": "#3e87b1ff",
         "terminal.ansi.magenta": "#39bae5ff",
         "terminal.ansi.bright_magenta": "#205a78ff",
-        "terminal.ansi.dim_magenta": "#addcf3ff",
+        "terminal.ansi.dim_magenta": "#2782a0ff",
         "terminal.ansi.cyan": "#95e5cbff",
         "terminal.ansi.bright_cyan": "#4c806fff",
-        "terminal.ansi.dim_cyan": "#cbf2e4ff",
+        "terminal.ansi.dim_cyan": "#68a08eff",
         "terminal.ansi.white": "#bfbdb6ff",
         "terminal.ansi.bright_white": "#fafafaff",
-        "terminal.ansi.dim_white": "#787876ff",
+        "terminal.ansi.dim_white": "#85847fff",
         "link_text.hover": "#5ac1feff",
         "conflict": "#feb454ff",
         "conflict.background": "#572815ff",
@@ -855,31 +855,31 @@
         "terminal.background": "#242835ff",
         "terminal.foreground": "#cccac2ff",
         "terminal.bright_foreground": "#cccac2ff",
-        "terminal.dim_foreground": "#242835ff",
+        "terminal.dim_foreground": "#8e8d87ff",
         "terminal.ansi.black": "#242835ff",
         "terminal.ansi.bright_black": "#67696eff",
-        "terminal.ansi.dim_black": "#cccac2ff",
+        "terminal.ansi.dim_black": "#48494dff",
         "terminal.ansi.red": "#f18779ff",
         "terminal.ansi.bright_red": "#833f3cff",
-        "terminal.ansi.dim_red": "#fec4baff",
+        "terminal.ansi.dim_red": "#a85e54ff",
         "terminal.ansi.green": "#d5fe80ff",
         "terminal.ansi.bright_green": "#75993cff",
-        "terminal.ansi.dim_green": "#ecffc1ff",
+        "terminal.ansi.dim_green": "#95b159ff",
         "terminal.ansi.yellow": "#fecf72ff",
         "terminal.ansi.bright_yellow": "#937237ff",
-        "terminal.ansi.dim_yellow": "#ffe7b9ff",
+        "terminal.ansi.dim_yellow": "#b1904fff",
         "terminal.ansi.blue": "#72cffeff",
         "terminal.ansi.bright_blue": "#336d8dff",
-        "terminal.ansi.dim_blue": "#c1e7ffff",
+        "terminal.ansi.dim_blue": "#4f90b1ff",
         "terminal.ansi.magenta": "#5bcde5ff",
         "terminal.ansi.bright_magenta": "#2b6c7bff",
-        "terminal.ansi.dim_magenta": "#b7e7f2ff",
+        "terminal.ansi.dim_magenta": "#3f8fa0ff",
         "terminal.ansi.cyan": "#95e5cbff",
         "terminal.ansi.bright_cyan": "#4c806fff",
-        "terminal.ansi.dim_cyan": "#cbf2e4ff",
+        "terminal.ansi.dim_cyan": "#68a08eff",
         "terminal.ansi.white": "#cccac2ff",
         "terminal.ansi.bright_white": "#fafafaff",
-        "terminal.ansi.dim_white": "#898a8aff",
+        "terminal.ansi.dim_white": "#8e8d87ff",
         "link_text.hover": "#72cffeff",
         "conflict": "#fecf72ff",
         "conflict.background": "#574018ff",