Read spending from zenmoney in the poller, answer it from facts (#125)

The trust boundary is zenmoney, not maven — they already hold his bank
sessions. So the poller reads /v8/diff/ and writes totals as
facts(kind=env, source=poll:zenmoney); core reads those back when he asks
and never sees the token.

internal/zenmoney sums transactions per currency over a window, skipping
tombstoned rows and transfers between his own accounts, and refuses to
encode a summary built from zero transactions. That refusal is the whole
design: a failed or empty read writes nothing and leaves the last good
total alone, because a zero recited as fact is worse than silence. No
currency conversion either — a figure he can check against his bank beats
one he cannot.

Off unless configured, and the token is read from a FILE rather than a
flag so it never lands in `ps`, in docker-compose.yml, or in shell
history. Nothing about the money is search input, no tick rule reads the
keys, and the log lines name keys, never figures.

The live-credential half is BLOCKED: there is no zenmoney account or token
here, so everything is verified against a recorded diff fixture.

internal/router/money_test.go

@@ -0,0 +1,31 @@
+package router
+
+import "testing"
+
+func TestParseMoneyQuery(t *testing.T) {
+	cases := []struct {
+		in     string
+		window MoneyWindow
+		ok     bool
+	}{
+		{"сколько я потратил сегодня?", MoneyToday, true},
+		{"сколько я потратил в этом месяце?", MoneyMonth, true},
+		{"сколько я потратил?", MoneyMonth, true}, // month-to-date by default
+		{"покажи мои траты", MoneyMonth, true},
+		{"какие у меня расходы за месяц", MoneyMonth, true},
+		{"how much did I spend today", MoneyToday, true},
+		{"сколько я заработал в этом месяце", MoneyMonth, true},
+		// Not about money.
+		{"я потратил весь день на это", MoneyNone, false},
+		{"потратил много сил", MoneyNone, false},
+		{"какая погода?", MoneyNone, false},
+		{"я купил молоко", MoneyNone, false},
+		{"", MoneyNone, false},
+	}
+	for _, c := range cases {
+		w, ok := ParseMoneyQuery(c.in)
+		if ok != c.ok || w != c.window {
+			t.Errorf("ParseMoneyQuery(%q) = (%v, %v), want (%v, %v)", c.in, w, ok, c.window, c.ok)
+		}
+	}
+}