Hide transfers in the transactions view by default

Transfers move money between your own accounts; at 433 of 3,996 rows
(~11%) they crowd out the rows that represent actual spending.

getTransactions gains `exclude_categories`, opt-in per caller and
deliberately not defaulted in queries.ts: the rules preview and the bulk
rule-apply path both read candidate rows through getTransactions, and a
default exclusion there would silently shrink what a rule can see and
reach — invisibly, since a rule that matches nothing looks the same as a
rule with nothing to do.

Two behaviours the filter needs, both tested:

- An explicit category pick beats the exclusion. Selecting "Transfers"
  while the default is on subtracts it from the hidden list instead of
  returning zero rows and reading as "you have no transfers".
- COALESCE the effective category to '' before `<> ALL`. NULL <> ALL(...)
  is NULL, not true, so an uncategorised row would disappear from a
  filter that never named its category — the trap EXCLUDE_NON_SPEND
  already documents.

The default is off when the view is scoped to a statement: that is a
reconciliation view, the row count has to match the statement, and a
credit-card payment is the row you went there to check.

CLAUDE.md

@@ -95,6 +95,29 @@ COALESCE(o.merchant_normalized, t.merchant_normalized, t.merchant_name)  -- merc
 COALESCE(o.category_override, t.category)                                 -- category
 ```
 
+### Hiding categories in the transactions view
+
+`getTransactions` takes `exclude_categories`. It is **opt-in per caller and
+never defaulted in `queries.ts`** — `GET /api/rules/[id]/matches` and
+`POST /api/rules/apply` both read their candidate rows through `getTransactions`,
+so a default exclusion there would silently shrink what a rule can preview and
+reach. Only the transactions page sets it.
+
+The transactions view defaults it to `["transfers"]` (433 of 3,996 rows, ~11%),
+with a visible "Hide transfers" checkbox. Two rules the implementation depends
+on, both tested:
+
+- **An explicit category pick beats the exclusion.** Selecting "Transfers" while
+  the default is on subtracts it from the hidden list rather than returning zero
+  rows — otherwise the view reads "you have no transfers".
+- **`COALESCE(..., '')` before `<> ALL`.** `NULL <> ALL(...)` is NULL, not true,
+  so an uncategorised row would vanish from a filter that never named its
+  category. Same trap `EXCLUDE_NON_SPEND` documents.
+
+It defaults **off** when the view is scoped to a statement (`?statement_id=`).
+That is a reconciliation view — the row count has to match the statement, and a
+credit-card payment is exactly the row you went there to check.
+
 ## Database
 
 ```bash