Update create-dashboard skill: add visualization rules, workflow, and review checklist

[arsalann]

Summary

Update the create-dashboard skill (both .claude/skills/create-dashboard/SKILL.md and cmd/skill_templates/create-dashboard/SKILL.md) to a stronger version that emphasizes visualization quality, truthful charting, and a structured workflow — not just DAC authoring mechanics.

Motivation

The current skill is mostly a syntax reference. It describes how to write YAML/TSX, connections, and named queries, but does not guide the agent on:

• How to approach a dashboard analytically (question-first, inspect data, prefer few strong charts).
• Visualization best practices (truthful axes, no pie/3D defaults, accessibility, encoding clarity).
• A reproducible CLI workflow (dac validate → dac check → dac query → dac serve).
• A review checklist before declaring a dashboard done.

Result: agents currently produce technically valid dashboards that can still be misleading, cluttered, or under-explained.

Changes

Metadata

• Update description to mention semantic models, CLI validation workflows, and visualization design.

New sections

• Workflow — 8-step ordered process: inspect data → choose YAML/TSX → smallest dashboard → dac validate → dac check → dac query → dac serve --port 8321 (always surface http://localhost:8321) → visual review.
• Core Dashboard Rules — start from the analytical question; match chart type to task; make each chart self-explanatory (title, takeaway, sources, units, legend). Introduces the default 3-widget pattern: text title → chart → text footnote.
• Truthful Visualization Defaults — zero-baseline for bars/area, no pie by default, no 3D, no default dual y-axes, labeled log scales, sorted categorical bars, consistent comparison scales, explicit benchmarks, clear actuals vs forecasts.
• Accessibility And Readability — colorblind-safe palette, never color alone, legends/encoding keys, readable tooltips, no pre-truncated labels, no cramped charts, prefer direct labels when appropriate.
• DAC Guardrails — enumerated widget types, chart types, and the rule to only use supported schema properties.
• Query Sources — mutually exclusive list (query, sql, file, metric, direct semantic fields).
• Practical DAC Constraints — snake_case output columns, compensate for weak legends with nearby text, keep semantic logic declarative.
• Review Checklist — 10-point pre-signoff list.

Removed / simplified

• Drop .bruin.yml Connection Config section and themes/ layout entry (out of skill scope).
• Drop dac init from the commands block; add dac ls and a port flag (--port 8321).
• Drop the separate Semantic Dashboard YAML example; keep one focused YAML example using the title/chart/footnote pattern.
• Simplify the TSX example to one metric widget; remove duplicate authoring rules now covered by the checklist.
• Fold Named Queries into Query Sources.

Files touched

• .claude/skills/create-dashboard/SKILL.md
• cmd/skill_templates/create-dashboard/SKILL.md

Reference source for the new content: data_playground/shanghai-v1/.claude/skills/create-dashboard/SKILL.md.