fix(icons): replace hardcoded colors with currentColor for dynamic theming

Replace hardcoded stroke="#8C8D8F" and fill colors with currentColor
in all SVG icon files under public/icons/cortex/ (except file-types
which retain brand colors, and semantic icons like green-tick and
check-on which retain their fixed colors).

Icons updated:
- activity-bar/: 12 icons (stroke #8C8D8F → currentColor)
- navigation/: 15 icons (stroke #8C8D8F → currentColor, menu-left-on
  stroke/fill #FCFCFC → currentColor)
- actions/: 16 icons (stroke #8C8D8F → currentColor)
- status-bar/: 9 icons (stroke #8C8D8F → currentColor, excluding
  green-tick)
- sidebar/: 19 icons (stroke #8C8D8F → currentColor, filler fill
  #8C8D8F → currentColor, git-logo fill #FCFCFC → currentColor)
- chat/: 5 icons (stroke #8C8D8F → currentColor, code fill #CB93DE →
  currentColor, palette fill #6BBD8F → currentColor, brackets-square
  fill #E8DD9B → currentColor)

Also set CSS color property on CortexSvgIcon wrapper SVG element so
stroke="currentColor" in inner SVG content inherits the color prop
correctly.

Preserved:
- file-types/ brand colors (React blue, Rust logo, TOML colors)
- status-bar/green-tick semantic green (#018D0A)
- sidebar/check-on semantic blue (#008CFF)
- sidebar/magic-wand gradient fill
- sidebar/check-off structural opacity fill

Author: echobt

public/icons/cortex/chat/brackets-square.svg

@@ -211,6 +211,7 @@ export const CortexSvgIcon: Component<CortexSvgIconProps> = (props) => {
         display: "inline-block",
         "vertical-align": "middle",
         "flex-shrink": "0",
+        color: local.color ?? "currentColor",
         transition: "color 150ms ease",
         ...local.style,
       }}