Add view modal for saved responses

[rockfordlhotka]

Summary

• Added view button (👁️) to each saved response list item for previewing content without inserting into chat
• View modal renders full content as markdown in a scrollable panel with Back and Insert buttons
• Clicking item label still inserts directly into chat (unchanged behavior)
• Light and dark mode styles included

Test plan

• Open saved responses list, verify view button appears alongside delete
• Click view button — verify content renders as markdown with label/agent/date header
• Click Back — verify return to list
• Click Insert into chat — verify item is inserted and modal closes
• Click item label directly — verify it still inserts without going through view
• Verify dark mode styling

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