Docs: TSC report for blockdiag to Mermaid migration

Docs: TSC report for blockdiag to Mermaid migration

Add a comprehensive report for the ONAP TSC covering:
- Background and rationale for the migration
- Audit results (5 repos, 9 diagrams)
- Before/after diagram comparisons with live mermaid renders
- Gerrit change status (4 merged, 1 WIP pending review)
- Build verification results
- Remaining work plan (32 config-only repo cleanups)
- Asks of the TSC

Issue-ID: CIMAN-33
Change-Id: Ic492d849d9b067cb2b2222193d6dd0e3fbbbfb9c
Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Matthew Watkins <mwatkins@linuxfoundation.org>