Empty JSON array ([]) as a lookup-table reference file causes a confusing IntegrityError

**Where:** `astrodbkit.astrodb.Database.load_table()` (in the `astrodbkit` package, not this repo) does `conn.execute(self.metadata.tables[table].insert().values(data))` where `data` comes straight from `json.load()`. If the JSON file's top-level array is empty (`[]`), SQLAlchemy's `insert().values([])` is interpreted as "insert one row using column defaults" (a known SQLAlchemy quirk: an empty list to a multi-row `.values()` isn't a no-op), not "insert nothing."

**What happened:** After emptying `Publications.json`, `SourceTypeList.json`, and `ParameterList.json` to `[]` (clearing stale template-example placeholder rows before real data existed), `build_db_from_json()` failed with `sqlite3.IntegrityError: NOT NULL constraint failed: Publications.reference` — a single default-valued row was attempted, which violated the non-nullable `reference` column. The error message gives no hint that the root cause was an empty-array JSON file rather than a real data problem.

**Workaround:** Deleted the three now-empty JSON files entirely instead of leaving them as `[]` — `load_table()`'s existing `if os.path.exists(filename):` guard cleanly skips a missing file (with an optional verbose "not found" message), which is the actual correct way to represent "no data yet" for a reference table.

**Suggested change:** Either (a) `astrodbkit.astrodb.Database.load_table()` should special-case `if not data: return` before calling `insert().values(data)`, or (b) any astrodb-bot skill/reference doc describing the `data/reference/*.json` convention should explicitly say "represent an empty table by omitting the file, not by writing `[]`" so users don't hit this SQLAlchemy quirk.

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_Reported from a gotchas.md log filed by a skill user (2026-08-28)._

Start with the described Database.load_table() entry point in the astrodbkit package and verify how json.load() data reaches insert().values(data) when the file contains []. Compare that behavior with the existing missing-file path and the astrodb-bot reference documentation. Done means empty reference data no longer produces a misleading IntegrityError, either through the package behavior or an explicit documented convention.

Written by the indexing model from the issue text.