feat(mcp): model-free document upload via signed URL (#1378)

* feat(mcp): model-free document upload via signed URL (#748)

Adds gnubok_create_document_upload + gnubok_complete_document_upload so
document bytes reach storage through a short-lived signed PUT URL and
never pass through the model context. Fixes silent base64 corruption on
real-size PDFs and the context blowup on batch uploads.

- pending/ staage keys with TTL cleanup; completion validates magic
  bytes + SHA-256, moves bytes to the WORM key and adopts the reserved
  UUID as document id, making retries and concurrent completions
  idempotent
- legacy gnubok_upload_document kept for clients without file access,
  description now points to the signed-URL pair; shared mime resolution
  and inbox-item creation extracted
- both new tools mapped in TOOL_SCOPE_MAP (transactions:write) and
  MCP_TOOL_CAPABILITY_MAP (ai) so the paywall and scope gates hold
- payload guard ceiling 58.5K to 59K after trimming the create tool's
  outputSchema to upload_id/upload_url/expires_at

Fixes #748

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

* fix(mcp): satisfy capability-map lock and phantom-column scanner

The exact-entries lock in capability-maps.test.ts now includes the
signed-URL pair as dispatch-only AI tools, and the inbox insert uses a
literal payload (explicit UUID instead of a conditional spread) so the
no-phantom-columns scanner can resolve every column.

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

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/auth/api-keys.ts

@@ -232,6 +232,8 @@ export const TOOL_SCOPE_MAP: Record<string, ApiKeyScope> = {
   // Staged bulk retag of posted-line dimensions (dimensions PR6).
   gnubok_tag_journal_lines:               'bookkeeping:write',
   // Document inbox
+  gnubok_create_document_upload:          'transactions:write',
+  gnubok_complete_document_upload:        'transactions:write',
   gnubok_upload_document:                 'transactions:write',
   gnubok_list_inbox_items:                'transactions:read',
   gnubok_get_inbox_item:                  'transactions:read',