Add fullscreen controls to Mermaid diagrams

[davidmoshal]

Follow-up to #14, which shipped Mermaid rendering in v0.9.0.

Summary

• Open rendered Mermaid diagrams in an accessible viewport-filling dialog.
• Add toolbar, wheel, drag, pinch, and keyboard zoom/pan controls, including Fit and 100%.
• Restore the diagram and trigger focus on close, and close safely before theme rerenders.
• Keep the local viewer and interactive HTML exports identical through the shared Vite-built viewer assets.
• Preserve strict Mermaid rendering and readable invalid-diagram fallback behavior.
• Add permanent Chromium E2E coverage and update the command, exporter, and changelog documentation.

Validation

• pnpm test:web
• pnpm test:cli
• pnpm build:web
• pnpm build:cli
• go test -race ./packages/cli/cmd/openknowledge
• pnpm test:browser (8/8)
• openknowledge validate Wiki
• exact-SHA goal, QA, code-quality, security, and context reviews plus a runtime audit

No dependency or lockfile changes are included.

[filipdanisko]

@davidmoshal Thank you for the contribution, was thinking about adding myself! Will take a look at this soon!

[davidmoshal]

@filipdanisko — I’m Codex, the coding agent assisting @davidmoshal. I’m sorry for the confusion I caused on this PR.

After Mermaid rendering shipped in v0.9.0, I force-pushed this branch and changed #15 from the original rendering fix into a separate fullscreen/zoom enhancement. I should instead have closed the superseded PR and opened a clean follow-up against current main. Rewriting this PR’s scope and history created unnecessary review noise.

The follow-up is now separated into #16, containing only click-to-fullscreen Mermaid viewing with zoom, pan, Fit, and 100% controls. Issue #14 remains resolved by v0.9.0, and I’m closing this PR as superseded.

Thank you for the project, and apologies for the inconvenience.