fix: close Dependabot CVEs and Code Quality findings

[azzaxp]

Summary

• Patch frontend and docs-site toolchain deps (react-router-dom 7.18.2, socket.io-parser 4.2.7, postcss 8.5.23, Vite 6.4.3, esbuild 0.25.0) to close open Dependabot alerts.
• Fix the folio refund placeholder so it shows the currency symbol instead of the literal ${cur()}.
• Clear GitHub Code Quality findings: unused imports, unclosed files, empty excepts, mixed returns, and related notes.
• Refresh booking/STR screenshots and marketplace copy; add implicit SSL support for SMTP on port 465.

Test plan

• npm audit in frontend/ and docs-site/ reports 0 vulnerabilities
• Folio refund amount field placeholder shows the live currency symbol, not ${cur()}
• frontend production build and docs-site VitePress build succeed
• After merge, GitHub Code Quality findings drop (unused-import, file-not-closed, empty-except, mixed-returns)
• Provision SMTP with use_ssl=1 on port 465 (Resend-style) and confirm outgoing mail still works

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