refactor: split viewport and infinite canvas modules

[markm39]

Summary

• Split ZoomableInkViewport into a thin render/controller shell, pure geometry helpers, and a dedicated gesture hook for pinch, pan, tap, momentum, and transform notifications.
• Split InfiniteInkCanvas public types, defaults, notebook/page helpers, page-stack rendering, and styles into focused infinite-ink-canvas modules.
• Added src/infinite-ink-canvas to the published package file list so React Native source consumers receive the new internal modules.

Test plan

• npm install
• npm --prefix example install
• npm run typecheck
• npm test -- --runInBand
• npm run test:native:smoke
• npm run test:example:typecheck
• npm run build
• npm run pack:dry-run
• npm audit --audit-level=moderate
• Simplify review completed; preserved page-stack memoization after extracting render components.
• Security review completed for the changed code; no new dynamic-code, secret, bridge, or package exposure issues found.
• App/device verification intentionally not run per maintainer request; maintainer will run it after this PR.
• npm --prefix example audit --audit-level=moderate still reports the pre-existing Expo/PostCSS advisory (GHSA-qx2v-qp2m-jg93) that requires separate dependency work outside this refactor.