Explore sixel for dashboard rendering

[sentry-junior]

Investigate using sixel (or similar terminal graphics protocols) for dashboard view rendering.

• Today dashboards render through a character framebuffer + ASCII/sparklines in src/lib/formatters/dashboard.ts
• That works for tables and basic charts, but is a weak fit for denser visuals (heatmaps, multi-series charts, wheel, etc.)
• Sixel could give pixel-level output in capable terminals while keeping a plain-text fallback for others

Explore feasibility and tradeoffs:

• terminal support matrix (iTerm2, Kitty, WezTerm, Windows Terminal, tmux/ssh)
• how sixel would plug into the existing grid/framebuffer layout
• dependency/runtime cost and graceful fallback when unsupported
• whether this should be opt-in (--graphics=sixel) or auto-detected

Requested by byk via Junior.

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View Junior Session in Sentry