Pins: bump mermaid-cli to 11.12.0 and align Chromium revision; re-render diagrams

[flyingrobots]

Summary\n- Bump MERMAID_CLI_VERSION to 11.12.0 (current latest) in scripts/pins.sh and CI.\n- Determine Puppeteer version bundled by mermaid-cli@11.12.0 and set CHROMIUM_REVISION accordingly (or compute dynamically in CI).\n- Re-render all diagrams and commit updated SVGs with new mermaid-meta (cli=11.12.0).\n- Update CI cache keys to include new revision.\n\nRationale\n- Keep up with security and bug fixes in mermaid-cli/puppeteer.\n- Avoid drift between local scripts and CI by centralizing pin reads (done in this PR).\n\nAcceptance\n- CI diagrams job passes generation + verify.\n- No functional regressions in diagrams; any intentional visual diffs are reviewed.\n\nNotes\n- Transitional variable MERMAID_CLI_PREV_ALLOW can be set to 10.9.0 temporarily to smooth verify during the changeover, but final state should remove it.\n