feat: align final input chunks and clarify the public API

[dkulyk]

Passing a final chunk to a manager's end(chunk) silently discarded it in JavaScript, while core and Node inputs accepted that pattern. Record managers, prefix filters and decoded-input adapters now consume an optional final text/UTF-8 chunk before flushing and EOF validation. Final-chunk input uses the same type, mode, reentrancy and failure checks as write(); no scanner hot loop changes.

Reorganize documentation around ordinary developer tasks: selected values, root retention, streaming strings, Web/Node input and JSONL. Add a methods/properties/options reference and error-ownership table; move plans/boundaries/reset to Advanced, migration to its own page, and contributor tooling to CONTRIBUTING. Keep old guide anchors as short navigation links and include new public pages in the npm archive. README shrinks from 82 to 64 lines.

Clarify that fulfilled getValue() promises cannot be revoked by later syntax errors and do not prove whole-input validity. Add complete string/Web/Node examples, explicit async rejection ownership, and JSDoc for public methods and defaults. Mark final chunks on adapters/managers as unreleased since published beta.1; no release version or existing archive/tag changed.

Validation:

• 519 tests pass on Node and actual Bun, including final text/byte chunks at every Unicode cut, mixed/invalid-input retries, truncated UTF-8, duplicate EOF and reentrancy.
• Build, Biome and packed type-resolution checker pass; type fixtures cover text-only and byte-capable final chunks.
• Smoke passes on Node/Bun/Deno and includes the new final-byte-chunk regression; fresh installed archive passes ESM/CJS smoke and strict TypeScript checks.
• Executed 9 README/guide examples and checked 36 local documentation links/anchors.

Existing subscription names and callback timing are preserved. Internal declaration facade isolation remains a separate follow-up; no breaking observer-type split is introduced.

Remote CI passes on Node 22/24, Bun and Deno; CodeQL passes for JavaScript/TypeScript and Actions.