Cut 16.2.0 and bump the package version in pyproject.toml, uv.lock, and
CITATION.cff.

Minor: Add opt-in uuid_on_collision=merge for Graph configs with uuid_fields
(#126). Divergent same-id edges now union list fields deterministically, keep
first scalar values while counting conflicts, retain fields introduced by later
records, and preserve first-seen output order; default error mode and streaming
memory behavior remain unchanged. The merge mode is rejected without
uuid_fields as uuid-merge-without-fields.

Changelog:
- Versioned the 16.2.0 Unreleased section as 16.2.0 - 2026-09-03; the entry
  already cites #126.

Docs: The PR already documented uuid_on_collision in
docs/configuration/graph.md and docs/api/utils.md; no additional docs changes
were needed here.

Testing:
- uv run pytest -q -> 1119 passed, 15 skipped (94% coverage)
- uv run ruff check . && uv run ruff format --check . && uv run pyright ->
  clean / 0 errors, 0 warnings, 0 informations
- uv lock --check -> up to date (167 packages resolved)
- uv run mkdocs build --strict -> clean