Intake: bulk upload + auto-classification + assign-or-create flow

Adds an /intake triage queue for bulk-uploaded contracts. Each upload is
classified by an LLM and routed to an existing project (counterparty
match) or a new one with a single click.

Schema:
- documents.intake_role / intake_status / intake_counterparty /
  intake_parent_counterparty / intake_lifecycle_hint / intake_confidence /
  intake_analyzed_at.

Backend:
- New lib/intakeAnalysis.ts: maybeAnalyzeIntake() runs one LLM call that
  determines role (buyer/seller/mutual), status (draft/execution/unknown),
  counterparty, parent entity, lifecycle position (original/amendment/
  renewal/addendum/sow/order_form/etc.), and self-reported confidence.
- Hooked into POST /single-documents and POST /projects/:id/documents,
  fire-and-forget alongside contract-fact extraction.
- GET /single-documents/intake returns pending docs + the user's projects
  for client-side counterparty matching.
- POST /single-documents/:id/assign accepts {project_id} OR
  {new_project: {name, template, counterparty, parent_counterparty}}.

Frontend:
- New /intake route with bulk upload button (multi-file).
- Per-doc row shows role + status + lifecycle pills, counterparty +
  parent + confidence, fuzzy-matched existing project suggestions
  (single click to assign), and a "Create new project" button that
  preselects the right template based on detected role.
- AppSidebar gains Intake entry above Projects.
- Polls every 4s while any doc is mid-analysis.