docs: unify user journey and clarify build and early deployment flow

[GandholiSarat]

This PR refines the structure and navigation of the DynamoRIO documentation by establishing a canonical end-to-end User Journey on the home page and aligning the build and deployment guides with that flow.

The build documentation is reorganized to clearly separate quick-start guidance from advanced build scenarios, and to explicitly document build layout, install outputs, and platform/architecture scope. Runtime validation steps are removed from the build flow to keep build and execution concerns distinct.

The deployment documentation adds concise execution context, including where drrun comes from, how the launch models differ (drrun, drconfig, drinject), and what constitutes a first successful run. Platform-specific deployment content (Android, QEMU) is grouped under an advanced section, and attach behavior is consistently marked as experimental.

The Build Your Own Tool page is kept focused on client APIs and concepts, with a short reference to the canonical User Journey rather than duplicating workflow steps.

Documentation only; no API, tooling, or behavioral changes are introduced.

[GandholiSarat]

Thanks for the review. I’ve applied all the suggested clarifications, fixed stale Doxygen references, and ensured the docs build cleanly. Please let me know if anything else needs tweaking.

[GandholiSarat]

Thanks — I’ve moved the Debug Build subsection back under Advanced Build Scenarios

[derekbruening]

Thank you for improving the documentation.

I wish the review process included a way to preview the final html view of the docs but that's not simple: please double check after running ci-docs that the section hierarchy and html generation is all as desired.