Make the naming scheme fully user-editable, with the user's preferred format as default

- ExpressionFormat::compile_scriptlet now falls back to treating a {token} as a
  literal multi-word binding key when it's neither a valid Rhai identifier nor
  valid Rhai script, but still looks like a plain human-typed field name (only
  letters/digits/underscores/spaces). This is what lets `{show name}` work
  without anyone needing to know Rhai, while real Rhai script (even containing
  spaces) still takes priority and genuine syntax errors still surface.
- New default naming scheme app-wide: `{show name} - {season number}x
  {episode number} - {episode name}` (previously the terser {n} - {s00e00} -
  {t} form). Match/Fetch Data auto-upgrade targets updated to match, and
  sample items carry both the short FileBot-style keys and the new
  human-readable ones side by side.
- Naming scheme editor UI rewritten: explains the field is fully editable,
  lists available fields grouped by when they become available (always /
  after Match / after Fetch Data), and clarifies Rhai script is also
  supported for anyone who wants it.
- 3 new unit tests for the plain-field-name fallback (multi-word lookup
  works, real Rhai still takes priority, genuine syntax errors still error).

src/components/RenamePanel.css

@@ -262,6 +262,59 @@
   line-height: 1.5;
 }
 
+.format-hint code,
+.format-editor label code {
+  background: rgba(255, 255, 255, 0.06);
+  border-radius: 4px;
+  padding: 1px 5px;
+  font-family: ui-monospace, "SF Mono", monospace;
+  font-size: 10.5px;
+  color: var(--text);
+}
+
+.format-hint a {
+  color: var(--aurora-cyan);
+}
+
+.format-fields {
+  margin: 10px 0 0;
+  display: flex;
+  flex-wrap: wrap;
+  gap: 10px;
+}
+
+.format-fields-group {
+  flex: 1 1 160px;
+  min-width: 140px;
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 5px;
+  padding: 8px 10px;
+  background: var(--surface);
+  border: 1px solid var(--surface-deep);
+  border-radius: 8px;
+}
+
+.format-fields-group-title {
+  flex-basis: 100%;
+  font-size: 10px;
+  font-weight: 700;
+  text-transform: uppercase;
+  letter-spacing: 0.03em;
+  color: var(--muted-text);
+  margin-bottom: 2px;
+}
+
+.format-fields-group code {
+  background: rgba(255, 255, 255, 0.06);
+  border-radius: 4px;
+  padding: 2px 6px;
+  font-family: ui-monospace, "SF Mono", monospace;
+  font-size: 10.5px;
+  color: var(--aurora-green);
+}
+
 .modal-overlay {
   position: fixed;
   inset: 0;