Run View: finish accessibility and credential safety

[5aumit]

What to build

Polish the complete Run View across screen sizes, input methods, themes, and security boundaries.

Blocked by

#7, #8, and #9.

Acceptance criteria

• The B split view becomes one usable column on narrow screens without horizontal overflow.
• All actions and expandable regions are keyboard operable with visible focus.
• Reduced motion removes nonessential animation without delaying true completion.
• Light and dark modes remain coherent through Gradio theme variables.
• Gemini credentials remain session-only and absent from Search Briefs, Run Events, Results,
  replay fixtures, URLs, logs, and persisted presentation state.
• Full lint and test suites pass without flaky browser behavior.
• Manual E2E inspects desktop, narrow, light, and dark states with PR screenshots or a short
  recording.

[5aumit]

Planning update

The full accessibility and credential-safety work stays after #9.

The release-blocking layout overflow has been pulled into #19 so it can be fixed earlier without prematurely taking on this issue’s full scope. After #9, finish the remaining keyboard, focus, reduced-motion, theme, credential-retention, and manual E2E checks here.

The ready-for-agent label is removed because #8 and #9 are still open.

[5aumit]

Current-code references

• The split Results layout has fixed minimum grid widths, while its narrow-screen rule only changes the inner grid: setscout/presentation.py:31-37 and setscout/presentation.py:89-112.
• The visible Run Activity region is repeatedly rendered with aria-live="polite": setscout/presentation.py:147-162.
• The API-key entry point is the password-mode Gradio textbox: app.py:194-204. This is a code pointer only. Credential retention still needs explicit verification.

#19 now owns the immediate overflow fix. This issue retains the broader accessibility and credential-safety work.