feat(data): add DAC as an open-source Tableau alternative

[arsalann]

Adds DAC to data/tools.json under Analytics, and lists it in Tableau's alternatives array.

DAC is a dashboard-as-code tool: dashboards are defined in YAML or TSX files, stored in git, and served by a single Go binary. It has a built-in semantic layer for defining metrics and dimensions once and reusing them across widgets, and connects to Postgres, MySQL, Snowflake, BigQuery, Redshift and Databricks.

Against CRITERIA.md:

• Active maintenance — commits daily; last commit 2026-08-19; tagged releases.
• Open source license — AGPL-3.0.
• Self-hostability — single self-contained Go binary you run on your own machine or server; no vendor callback. Docker config not included in this PR.
• Functional replacement — replaces the core Tableau workflow (connect to a warehouse, define metrics, build and serve dashboards), for teams that prefer version-controlled definitions over a drag-and-drop editor.
• Community traction — 728 GitHub stars.

Scope: one tool, one category, plus the single alternatives reference. I did not touch the generated tools-min.json / tools_expanded*.json files — let me know if you want those regenerated in this PR. data/tools.json still parses as valid JSON (146 entries).

Disclosure: I work on the team that builds DAC.