v0.2.3 — tray agent monitor, chat search, preview mermaid/CSV, browser links

What's new

• Tray agent monitor: running agents with log tails, Stop agent, and a badge when one finishes
• Chat search: Ctrl/Cmd+F quick search with live highlighting (never touches the message DOM)
• Preview tab: mermaid diagrams, CSV/TSV tables with line/bar charts, shiki syntax highlighting for source files
• Diagrams in answers: mermaid and CSV fences in chat render inline
• Links: external links open in the system browser
• Image drop: dragging an image into the window attaches it to the composer
• Explorer panel now opens on the workspace instead of freezing on the home fallback