fix(import): repair the bulk import that cloned 38 repos but created zero DB rows #3527

The first real bulk run against ccantynz-alt cloned every repo to disk and created zero DB rows. Three fixes in importOneRepo:

1. ON CONFLICT vs partial index. repos_owner_name is partial (WHERE org_id IS NULL, migration 0004). ON CONFLICT (owner_id, name) without the predicate makes Postgres reject the whole insert — "no unique or exclusion constraint matching the ON CONFLICT specification" — and it threw after the clone landed. Now passes where: org_id is null.

2. Orphan adoption. Destination dir present with commits but no DB row = a prior run died after the clone. Adopt it (insert the row, skip the re-download) instead of dying on "destination path already exists". Empty leftovers are removed and re-cloned.

3. Case-insensitive existing check. Pre-import repos stored with original casing (ccantynz/Vapron) were invisible to the exact-match check, so run 1 cloned a duplicate vapron.git beside Vapron.git. Now compares lower(name).

bun test import suites 11/11, tsc clean.

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