Improve active tab indication when using color-coded tabs (APP-4321)

[warp-dev-github-integration]

Description

Fixes APP-4321.

When tabs are color-coded (manually via the right-click color picker or automatically via Directory tab colors), the active tab can be hard to tell apart from inactive colored neighbours. The active state used a only-modestly-brighter fill and shared the same neutral gray border with every other tab.

This PR strengthens the active state in both tab layouts:

Standard (horizontal) tab bar (app/src/tab.rs):

• The active colored tab's fill opacity is bumped (60 → 85 with NewTabStyling, and 50 → 80 in the legacy bar) so the active tab is clearly brighter than hovered/inactive neighbours. The legacy bar previously used the same opacity for active and hovered, which collapsed those two states.
• When the active tab is colored, its border is now drawn in the tab's own color at high saturation instead of the generic neutral overlay, giving the active colored tab a strong same-hue outline. Inactive colored tabs keep the existing subtle overlay border.

Vertical tabs (app/src/workspace/view/vertical_tabs.rs):

• The previously merged hover/selected fill opacity is split into three distinct levels (inactive: 15, hover: 35, selected: 75) so a selected row is clearly brighter than a merely-hovered row.
• When a selected row is colored, its border uses the row's own ANSI color at high saturation rather than fg_overlay_3, again so the active colored row pops against inactive colored siblings.

Behavior for tabs without a custom color is unchanged. All new colors are derived from the existing ANSI palette, so they remain theme-aware and work in light and dark themes.

Context: this builds on the prior work in APP-3905 (vertical-tab fill intensity bump) and APP-3863, both of which only partially addressed the original feedback.

Testing

• cargo check -p warp
• cargo fmt -p warp
• cargo clippy -p warp --all-targets --tests -- -D warnings
• Manual testing left for review (the change is purely visual; logic affects only the fill/border opacities of an already-rendered tab).

Server API dependencies

No server API dependencies.

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

Changelog Entries for Stable

CHANGELOG-IMPROVEMENT: Make the currently active tab easier to identify when tabs are color-coded by giving the active tab a brighter fill and a saturated colored border in both the standard and vertical tab bars.

cc @vkodithala

Conversation: https://staging.warp.dev/conversation/1689dae4-b7e3-4f5a-acd0-adb0d189cc66
Run: https://oz.staging.warp.dev/runs/019dd72f-77bf-791f-a3d7-2325b0dae6bd

This PR was generated with Oz.

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