[upstream #16545] Default dark avatar glyph sits at 2.6:1 on its fill #207

The default user avatar in the bundled dark theme paints its glyph in text-primary (#ececec) on the avatar-fill (#7989ff), 2.6:1 against the 3:1 floor WCAG 1.4.11 sets for graphical objects. LibreChat-AI#16545 gives the avatar its own avatar-fill and avatar-text roles and keeps these pixels on purpose, so the dark default is excluded from the 3:1 check in packages/client/src/theme/semanticTokens.spec.ts and pinned at no less than 2.6:1 instead.

The glyph is decorative (the avatar is aria-hidden next to the account name), so this is a visual refinement, not a blocker. Raising it means choosing a new dark avatar-text or avatar-fill default (for example a darker fill, or white at 3.07:1), which changes the default look and needs a design decision. Once done, restore the dark theme to the 3:1 describe.each list and drop the 2.6 pin.