refactor(ssr): Phase 8 — migrate New/Edit Invoice onto the engine (conditional :next)

The hardest modal in the app: one wizard that both creates and edits invoices,
with a conditional middle step (basic-details → [accounts] → next-steps, where
the expense-accounts step is skipped on the default-accounts path). Migrated off
mm/* + form-cursor + the EDN snapshot onto the session-backed engine (wizard2).

Finding: the OLD basic-details "Save" was broken. It hx-puts /invoice/new/navigate,
whose `[:to {:optional true} …]` query-schema 500s on empty query-params — Ring's
wrap-params yields {} for a no-query PUT, and main-transformer's parse-empty-as-nil
decodes {} → nil, which the bare [:map] rejects. Production uses the identical
wrap-params, so it was broken there too. So e2e/invoice-new.spec.ts is an ACCEPTANCE
gate (red on the old code, green on the engine, whose submit is a POST with no
query-schema): the migration fixes a latent bug. Create semantics (default → vendor
default account, location-spread; customize → posted grid; edit → prefill + updated
row) were pinned at the REPL.

What changed:
- defrecord 4 → 0 (NewWizard2 / BasicDetailsStep / AccountsStep / NextSteps), mm/ 0,
  fc/ cursor refs 0, step-params[…] field names 0.
- Conditional `:next` `(if (= :customize …) :accounts :done)` replaces mm/CustomNext +
  the broken 308-to-submit. Dual-purpose new+edit = one :init-fn branching on a route
  :db/id; create-wizard! seeds :init-data as per-step step-data so edit opens populated.
- The broken new-wizard-navigate route is deleted; the genuine async helpers
  (account-prediction, due/scheduled-payment-date, location-select, expense total/balance,
  add-row) remain but read the posted flat form (+ ws/get-all for the cross-step total).
- next-steps becomes the done-fn's returned modal (Pay now / Add another / Close).
- Dates ride as java.util.Date (#inst) in step-data so it's EDN-safe across the
  non-terminal step (clj-time DateTimes break the cookie store).

Verification: full e2e suite 61/61 (58 prior + 3 new); maybe-spread-locations unit
test 6/6; create semantics + edit prefill confirmed at the REPL. Skill fed
(scorecard Phase 8, gotchas {}→nil 500 + #inst dates, form-vs-wizard conditional
:next + dual-purpose).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/cljc/auto_ap/routes/invoice.cljc

@@ -15,7 +15,6 @@
                      :put ::new-invoice-submit
                      "/due-date" ::due-date
                      "/scheduled-payment-date" ::scheduled-payment-date
-                     "/navigate" ::new-wizard-navigate
                      "/account/new" ::new-wizard-new-account
                      "/account/location-select" ::location-select
                      "/account/prediction" ::account-prediction