[van-geaux]

Summary

• Add a provider-neutral EPUB bookmark contract and reader actions, with BookOrbit endpoints, payloads, and parsing owned by provider/bookorbit.
• Add Kavita PToC text bookmarks for list/add/open/delete, mapping XHTML reading-order pages and BookScrollId selectors to Readium locations. Kavita title/note editing remains unsupported; Komga reports bookmarks unavailable.
• Include the Kavita implementation as the user-approved scope extension on this branch; issue BookOrbit Bookmarks #290 itself requests BookOrbit bookmarks.
• Update provider docs, checklists, and UI/manual test guidance.

Verification

• Full JVM unit suite: 1,323 tests, 0 failures, 0 errors, 0 skipped.
• :app:compileDebugKotlin, :app:compileDebugUnitTestKotlin, :app:compileDebugAndroidTestKotlin, and lintDebug passed.
• assembleDebug and assembleDebugAndroidTest passed. The instrumented tests were compiled/assembled, not run on a connected device.
• User confirmed on-device BookOrbit list/create/open/edit/delete and Kavita PToC list/add/open/delete with location mapping on 2026-11-03. Exact tested build, server labels, device, and evidence location were not supplied. Preview/Komga UI visibility and Kavita's unmappable-location error path were not checked in that run.
• Local debug APK: /projects/bookorbit-android-issue-290/app/build/outputs/apk/debug/Lagrange-debug-202611031554.apk (SHA-256 6272159a61856e4c39385fb620780b23d1f8416a1969789ec5b870b03dd95cdc). The user did not identify this as the build used for manual validation.

Closes #290