feat(workflows): wire booking document actions (prepare_invoice/contract + send_document)

Implements the draft-seam booking cutover so the booking_invoice_only flow
becomes enableable. The booking flows trigger on quote.accepted, so the run
entity is the quote:

- prepare_invoice: convertToInvoiceOnly({draft:true}) creates the invoice(s)
  on HOLD (scheduled_send_at NULL, status stays 'scheduled') so the scheduler
  never auto-sends before the review gate; crash-recovery recovers drafts by
  the quote's deal_uuid. Stores ids in ctx.vars.preparedInvoiceIds.
- prepare_contract: createFromQuote (idempotent via converted_contract_id).
- send_document: dispatches the prepared draft (invoice -> sendInvoice each id,
  contract -> sendContract).
- resolveActor: quote creator -> workflow creator -> first admin.
- prepare_contract/prepare_invoice/send_document removed from the enable-guard
  list; prepare_event/prepare_quote/prepare_gallery/reserve_date still guarded,
  so booking_full/booking_simple stay blocked until the event-path increment.

Fixes a latent single-connection SQLite deadlock these unattended paths would
hit: getAppSetting/logActivity/adminActor read or write the global db, which
deadlocks when issued inside an open knex transaction. Thread the active trx
through getAppSetting, logActivity, nextInvoiceNumber, nextContractNumber, the
spawnInstallmentInvoices audit log, and hoist adminActor before createFromQuote's
transaction. convertToInvoiceOnly now logs after commit and returns invoiceIds.

Adds bookingCutover integration test (hold-mode null send-at, normal scheduled
contrast, contract path no-deadlock) and a route test that the now-implemented
booking invoice actions can be enabled.

backend/src/database/db.js

@@ -645,8 +645,14 @@ async function ensureGlobalCategories() {
 }
 
 // Helper function to log activities
-async function logActivity(activityType, metadata = {}, eventId = null, actor = null) {
+async function logActivity(activityType, metadata = {}, eventId = null, actor = null, executor = null) {
   try {
+    // Callers issuing the log from inside a knex transaction must pass that
+    // trx as `executor`, otherwise the global-`db` insert tries to grab a
+    // second connection from the single-connection SQLite pool while the
+    // trx still holds it → deadlock. Defaults to the global db for the
+    // common after-commit / outside-trx callers.
+    const conn = executor || db;
     // actor_id is integer-typed; some legacy callers pass a hex-string
     // identifier (e.g. a 16-char guest fingerprint) which makes Postgres
     // throw "invalid input syntax for type integer" and drop the entire
@@ -659,7 +665,7 @@ async function logActivity(activityType, metadata = {}, eventId = null, actor =
     const actorName = actor?.name
       || (actorIdInt === null && rawId !== undefined && rawId !== null ? String(rawId) : null);
 
-    await db('activity_logs').insert({
+    await conn('activity_logs').insert({
       activity_type: activityType,
       actor_type: actor?.type || 'system',
       actor_id: actorIdInt,