docs: industry-agnostic positioning + 'Who is this for?' + comparison table

[intraq-dev-ai]

README improvements from the GitHub discoverability audit, aligned with our positioning:

• The repo is general-purpose — any industry. 'Who is this for?' and 'Use cases' are framed by role and capability (operations teams, platform/SaaS vendors, internal BI) and use-case, with no vertical lock-in. Any SQL-backed database works.
• Verticals are commercial-support only. A single soft line notes tailored, pre-built domain knowledge bases + support are available commercially at intraq.dev — without enumerating industries in the repo.
• Comparison table — intraQ vs Power BI / Metabase / Lightdash, for 'X alternative' search intent.

Skipped: star/issue badges (low counts hurt) and developer technical articles (off-strategy). Community files, releases, Discussions, and topics were already in place.