fix(sync): adopt server epoch on fresh install / empty push without c…

[najuna-brian]

Description

Fixes the first‑sync repository reset / wipe warning when the device has not actually asserted a repository epoch yet, but Synkronus is already on repository_generation > 1 (e.g. after a server reset).

What changed

• synkronus (Push): If the client sends no repository_generation (header/body) and records is empty, respond 200 with the server’s epoch and current version instead of calling ProcessPushedRecords with the parser’s default 1, which previously always failed the pre‑loop generation check against a higher server epoch.
• formulus: When storage has 1 but there is no observation cursor yet (@last_seen_version missing / empty / 0), omit repository_generation on requests so the server can treat the client as adopting the current epoch (same as a missing key).

Tests

• Go: TestPush_emptyRecords_missingRepositoryGeneration_ok
• TS: effectiveRepositoryGenerationForRequest unit tests

Closes #609

[r0ssing]

Looks great! Nice to have the push request behavior match the pull and attachment 🦒