Show skill indicator in session view when triggered

[TechWizard9999]

Shows a clear purple indicator with skill name in the session view when a skill is triggered.

Closes #274

Approach

• Use existing SDK signals: Detect skills via tool call tool === "skill"
• Lightweight state derivation: activeSkill() memo reads tool metadata/title for skill name
• Minimal UI touch: Reuse existing skill visual language (purple badge + Sparkles icon)
• Status clarity: Map skill tool to "Using skill" in run status

Changes

• packages/app/src/app/pages/session.tsx - Added skill indicator logic and UI
• packages/app/src/app/app.tsx - Fixed undefined isDemoMode() reference

Testing

Build Verification

• TypeScript compiles - pnpm typecheck passes with no errors
• Production build succeeds - pnpm build:ui completes successfully

Manual Testing

• Dev server runs - pnpm dev:ui starts without errors
• No console errors - Browser console is clean on page load
• UI renders correctly - Session view loads and displays properly

Code Review

• Follows existing patterns - Uses same purple styling as skill badges
• No breaking changes - Only additive changes
• Type-safe - Passes TypeScript strict mode

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

[benjaminshafii]

would appreciate a small gif screenshot to help get this in faster (+ seems there's a merge conflict)

thx for the pr!

[TechWizard9999]

Hi @benjaminshafii ,

I have updated and verified it also resolved merge conflict

1. Indicator Appearance: The purple skill indicator (✨ Using skill) appears in the bottom status area when a skill is triggered.
2. State Logic: The indicator correctly shows Using skill only while the tool is actually executing. As soon as execution finishes which is (Fast), it transitions to Responding.
3. Visuals: The purple background and sparkles icon match the skill UI language.

I've attached a recording showing the indicator and the screenshot

GIF:

ScreenShot:

Please check this and let me know if you want any changes

[TechWizard9999]

Hi @benjaminshafii ,
Could you review this I have added the gif and the screen shot ,
Please let me know if anything is there

[TechWizard9999]

Hi @benjaminshafii ,
Could you check this if possible