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>

CLAUDE.md

@@ -34,6 +34,23 @@ reproducible and retag stops being safe. Covered by `TestRetagRewritesEveryTag`.
 `index.db` at the root of the data directory and re-importing must reproduce
 everything, with nothing lost.
 
+**The index is a cache, so there are no migrations.** `store.Open` applies
+`schema` and nothing else — no `ALTER TABLE`, no version column, no repair of
+an index an older build wrote. Changing the schema costs one line in the
+release note: delete `index.db` and import again. The two directions are not
+symmetric, which is worth knowing before you assume something is broken:
+
+- *Removing* a column leaves an older index still working, carrying the dead
+  column and its data unread.
+- *Adding* one the code reads breaks every command against an older index with
+  `query transactions: SQL logic error: no such column: …` until it is deleted.
+
+That asymmetry holds only because every statement names its columns —
+**no `SELECT *`, and nothing may depend on column order.** Keep it that way.
+Do not reintroduce migration machinery either; if re-parsing ever becomes too
+expensive to ask for, that is a decision to revisit deliberately rather than a
+helper to slip back in.
+
 **Dedupe is by fingerprint**: `sha256(date | amount | normalised description |
 ordinal)`, where the ordinal distinguishes identical lines *within one
 statement*. Two identical purchases on one day both survive; the same line in an
@@ -123,6 +140,11 @@ money --root /tmp/.../demo import          # must report 0 new
 money --root /tmp/.../demo ls --wide
 ```
 
+If you changed the schema, delete that root's `index.db` first. Nothing
+migrates it, so a demo root left over from an earlier build either carries dead
+columns or fails with `no such column`, depending on which way the schema
+moved.
+
 ### Driving the TUI in tests
 
 Prefer feeding `tea.Msg` values to `Model.Update` directly — that is how every