docs(7138): rephrase fade rationale around busy-pad color collisions

Each faded author counts as a second on-screen color, so a 30-author pad
visually becomes a 60-color pad — that's the primary motivation for
disabling the fade. The previous wording only mentioned "users picking
light colors", which missed the larger reason and the "or just don't
want inactivity tracking" case.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

doc/docker.md

@@ -115,7 +115,7 @@ If your database needs additional settings, you will have to use a personalized
 | `PAD_OPTIONS_ALWAYS_SHOW_CHAT`   |             | `false` |
 | `PAD_OPTIONS_CHAT_AND_USERS`     |             | `false` |
 | `PAD_OPTIONS_LANG`               |             | `null`  |
-| `PAD_OPTIONS_FADE_INACTIVE_AUTHOR_COLORS` | Fade each author's caret/background toward white as they go inactive. Set to `false` if users pick light colors that become indistinguishable from the faded variants. | `true`  |
+| `PAD_OPTIONS_FADE_INACTIVE_AUTHOR_COLORS` | Fade each author's caret/background toward white as they go inactive. Set to `false` on busy pads (every faded author counts as a second on-screen color, so 30 contributors visually become 60), when users pick light colors that fade into the background, or whenever inactivity tracking is undesirable. | `true`  |
 
 
 ### Shortcuts

src/static/js/ace2_inner.ts

@@ -237,9 +237,10 @@ function Ace2Inner(editorInfo, cssManagers) {
     } else if (info.bgcolor) {
       let bgcolor = info.bgcolor;
       // padOptions.fadeInactiveAuthorColors (default true) controls whether the author
-      // background fades toward white as the author goes inactive. Integrators can set
-      // it to false server-side when users pick light colors that become indistinguishable
-      // from the faded variants.
+      // background fades toward white as the author goes inactive. Integrators set it to
+      // false on busy pads (each faded author is effectively a second on-screen color, so
+      // a 30-author pad becomes a 60-color pad), or when inactivity tracking is undesirable
+      // for whatever reason.
       const fadeEnabled = window.clientVars.padOptions == null ||
           window.clientVars.padOptions.fadeInactiveAuthorColors !== false;
       if (fadeEnabled && (typeof info.fade) === 'number') {