chore: delete the two SQLite databases committed into the tree

[ywatanabe1989]

Two real SQLite database files were tracked in this repository:

file	size
.scitex/clew/runtime/db.sqlite	69,632 bytes
examples/_legacy/scitex/clew/multi_parent/scitex/clew.db	94,208 bytes

Neither is referenced by any code. Both are stale artefacts of a clew runtime that no longer exists — and the repository already says so, in two places, without ever having removed them:

.gitignore:930            **/scitex/clew.db
.scitex/dev/config.yaml   "stale orphan dir (clew.db inside; ...)"

An ignore rule does not untrack a file that is already tracked. That is the whole story of how a 94 KB database sat in a Python package's examples directory while being explicitly ignored.

How the other one got in

.gitignore listed db.sqlite3 and db.sqlite3-journal but not db.sqlite, so .scitex/clew/runtime/db.sqlite matched nothing at all. This PR adds db.sqlite beside db.sqlite3 in both ignore blocks (lines 147 and 393) so the same one-character gap cannot be walked through again.

Verification

After this change, git ls-files filtered on \.db$|\.sqlite$|\.sqlite3$ returns nothing in this repository.

Scope

Part of the fleet-wide SQLite eradication. Deliberately not touched: scitex-db, crossref-local and openalex-local — named exceptions whose databases must survive.

[ywatanabe1989]

Closed by the SciTeX 72-hour freshness policy: this PR had no activity for more than three days. PRs are perishable inventory and green evidence ages with the base. If the change is still needed, create a fresh PR from the current base rather than reviving this stale integration state.