Add a rule builder screen with a live glob preview

Writing a glob by hand meant guessing what it would catch, then running retag
to find out. The new screen, on 4, puts the glob, account and tag fields on
the left and every still-untagged description on the right, sorted
alphabetically and grouped by description with an occurrence count.

Matches are marked as the glob is typed, along with a count, so the effect of
a rule is visible before it is written. Enter appends it to rules.toml via
config.AppendRule, reloads the engine from disk and retags, so the rows it
caught leave the list immediately.

Rules are appended rather than prepended, keeping the precedence of anything
already in the file. Since the preview only lists transactions no existing
rule has tagged, it reflects that precedence for free.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -47,6 +47,13 @@ conversion, and totals are never summed across currencies.
 
 **First matching rule wins**, so transfer rules belong above general tag rules.
 A rule setting several of `match` / `counterparty` / `type` requires all of them.
+`config.AppendRule` therefore appends — never prepends — so saving from the
+rule builder cannot shadow a rule the user wrote by hand.
+
+**The rule builder is a form, so the global keymap must not apply there.**
+`Update` routes to `updateRules` before `updateNormal` whenever the view is
+`viewRules`, or typing `q` would quit and `i` would start an import. Any new
+full-screen input needs the same treatment.
 
 ## Adding a bank parser