Drop schema migrations

The index is a cache. Everything in it is re-derived from the statements and
rules.toml, and has been since the last hand-set tags went, so keeping
machinery to nurse an old index through a schema change was paying for a
guarantee nothing needs. The ALTER TABLE lists, the dropped-column list and the
pragma_table_info reader are gone; Open applies the schema and returns.

What replaces it is a line in the release note: delete index.db and import
again. The two directions are not symmetric, which is worth knowing before
assuming something is broken. Removing a column leaves an older index working,
carrying the dead column and its data unread, because every statement here
names its columns -- that is why the drop half was never really load-bearing.
Adding a column the code reads breaks every command against an older index with
`no such column` until the file is deleted.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -23,6 +23,8 @@ tagged by glob rules you write.
 
 \* Nothing lives only in the index: it is derived entirely from the statements
 plus rules.toml, so deleting it and re-importing gets you exactly what you had.
+It is a cache and nothing more, which is why it is never migrated — if a new
+build changes its shape, delete it and run `money import` again.
 
 ## Where the data root lives