docs: market research enhancement + data sources inventory
- market-research-padel-costs-2026.md: add sections 11-15 (demand-side
city profiles, CAPEX breakdown by component, insurance benchmarks,
seasonal utilisation patterns by climate zone, Playtomic GMV data)
- data-sources-inventory.md: 27 data sources across 7 categories
(court locations, pricing, market reports, real estate, demographics,
regulatory, tournaments) with access method, license, and update freq
- CMS.md, I18N.md: feature documentation from template analysis
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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