docs: Align README with ISMS-PUBLIC standards and enhance documentation consistency (#722)

* Initial plan

* Enhance README with ISMS alignment, feature details, and documentation portal

Co-authored-by: pethers <1726836+pethers@users.noreply.github.com>

* Fix typos and cleanup duplicate documentation sections

Co-authored-by: pethers <1726836+pethers@users.noreply.github.com>

* docs: Add missing documentation sections from docs page (Security Architecture, Lifecycle, Financial, Threat Model, CRA)

Co-authored-by: pethers <1726836+pethers@users.noreply.github.com>

* docs: Fix URL consistency, add emoji to section heading, remove duplicate Features section

Co-authored-by: pethers <1726836+pethers@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pethers <1726836+pethers@users.noreply.github.com>

Author: Copilot