[FEATURE] niri template: tab-indicator active-color should contrast with the focus-ring

[brianhelba]

Submission checklist

• I have searched existing issues and confirmed this has not been requested before.
• I have checked existing pull requests for similar changes.

Feature type

UI / visual improvement

Feature summary

The niri template assigns {{colors.primary.default.hex}} to both focus-ring.active-color and tab-indicator.active-color. Since niri draws the tab indicator directly beside the window edge, a focused tabbed column shows the indicator flush against a same-colored focus ring, making the active tab marker effectively invisible.

Motivation / use case

With any scheme, the two elements answer different questions ("which window is focused" vs "which tab is active") and lose their meaning when identically colored. Discovered while theming niri with a custom scheme; reproduces with every built-in palette since the tokens are always equal.

Proposed solution

Use a contrasting Material role for the tab indicator's active color — colors.secondary fits well (analogous precedent: the mango template already distributes secondary/tertiary tokens across roles, PRs #3156/#3345). Applies to both the v5 template and the v4.7.7 template.

Alternatives considered

No response

References / related projects

No response

Additional context

No response