docs: improvement of architecture documentation (#483)

* docs: prepare improvement of arch overview

* Initial plan

* docs: add comprehensive architecture overview with package roles and build/runtime stages

Co-authored-by: jankapunkt <1135285+jankapunkt@users.noreply.github.com>

* docs: add Key Terms section explaining Spacebars, Template, Template Instance, and View

Co-authored-by: jankapunkt <1135285+jankapunkt@users.noreply.github.com>

* docs: fix relationship diagram to accurately show Template Instance references View

Co-authored-by: jankapunkt <1135285+jankapunkt@users.noreply.github.com>

* docs: remove redundant info

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Nacho Codoñer <igcogi@gmail.com>

Author: 3 people