feat(realtime): attach primary-key realtime writers

[HaHaJeff]

Part 6/9 of the primary-key realtime stack.

Depends on: #10

What is this PR for?

Build the primary-key realtime path as one reviewable layer of the stack.

What changes?

Connects primary-key realtime writers to file-store writes and commit preparation. Adds validation for supported primary-key realtime options and focused write, schema, and utility coverage.

Tests

• Restack validation: every commit prefix was built and its focused tests passed.
• Stack-wide validation: the final realtime integration suite passed 58/58, the primary-key integration slice passed 16/16, and the full pre-commit run passed all nine hooks.
• Post-seal validation: the focused WAL replay test was rebuilt and passed after the final formatting amend.