[uyg7x]

Closes #6901

Adds the 21 src/ directories that were missing from docs/architecture.mermaid, using the grouping proposed in the issue.

• Adds 7 nodes: KUNA, ANDROID_TOOLS, CAPTURE_TOOLS, NATIVE_READERS, FORMAT_READERS, RUNTIME, FILESYSTEM
• Adds 20 arrows. No existing lines were changed (git diff --stat: 28 insertions, 0 deletions)
• All 51 src/ directories are now represented in the diagram
• All arrow targets resolve to defined nodes; subgraph/end balanced (11/11)
• Verified the diagram renders cleanly with @mermaid-js/mermaid-cli

The grouping is a suggestion — happy to split or fold nodes on request.

cc @CassieFox23 (original proposal)

Author readiness

Human owner: @uyg7x

• I reviewed the final diff and relevant existing code, understand the change and its edge cases, and take responsibility for the complete PR, including AI-assisted work.
• I checked the evidence above, confirmed it supports the current change, and recorded meaningful validation gaps.
• I declare this PR ready for initial maintainer review.