Batch Analyse requests and survive opaque provider schema budgets

Analyse now classifies up to ten same-kind transactions per provider
request: the registry and history travel once per batch, so a
thousand-row backfill costs about a hundred paced requests instead of a
thousand. The answer schema appears once — an array item carrying an
enum-bound ref — because providers meter strict schemas by token cost:
duplicating registry enums per row, or bounding arrays with
minItems/maxItems that Gemini expands per element, rejects real
registries with a bare HTTP 400. Row count, duplicate refs, duplicate
tags and taxonomy bounds are all enforced server-side instead, and a
request still rejected outright halves until accepted, remembering the
working size for the run. Batch requests scale the HTTP budget by row
count, chunk failures cannot abort a run whose later rows succeeded,
and rows resolved against one snapshot share one minted merchant.

Measured on a real 165-row month over a zero-data-retention route:
165 analysed, 152 proposals, 0 errors, 17 requests, under 8 minutes.

Fresh installs default to google/gemini-3.8-flash, the model that
demonstrably honors strict structured outputs over a ZDR route. Preview
changes now carry counterparty, amount and currency, and the review
list shows the amount with a counterparty fallback for banks that leave
descriptions empty.

internal/app/app.go

@@ -141,6 +141,12 @@ func Open(dir string) (*App, error) {
 	} else if !os.IsNotExist(e) {
 		return fail(e)
 	}
+	// A fresh install classifies with a fast, inexpensive model that
+	// demonstrably honors strict structured outputs over a zero-data-retention
+	// route; an explicit config.toml entry always wins.
+	if strings.TrimSpace(a.settings.Model) == "" {
+		a.settings.Model = "google/gemini-3.8-flash"
+	}
 	if b, e := os.ReadFile(filepath.Join(dir, "state", "sync-state.json")); e == nil {
 		if err = json.Unmarshal(b, &a.ops); err != nil {
 			return fail(fmt.Errorf("sync state: %w", err))