Add job brackets for grouping multi-part or repeated jobs

- JobBracket model: name, customer, notes
- Migration 0006: job_brackets table + bracket_id FK on print_jobs
- /brackets: list with per-bracket progress bar
- /brackets/{id}: detail with jobs table + Add Job(s) modal (quantity field
  creates N identical jobs in one shot, each with its own UUID and log entry)
- /jobs Add Job modal: optional bracket selector
- Sidebar: Brackets nav item added

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/models/job_bracket.py

@@ -0,0 +1,21 @@
+from datetime import datetime
+
+from sqlalchemy import DateTime, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class JobBracket(Base):
+    __tablename__ = "job_brackets"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    name: Mapped[str] = mapped_column(String(200))
+    customer: Mapped[str | None] = mapped_column(String(200))
+    notes: Mapped[str | None] = mapped_column(Text)
+    created_at: Mapped[datetime] = mapped_column(DateTime, server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime, server_default=func.now(), onupdate=func.now()
+    )
+
+    jobs: Mapped[list["PrintJob"]] = relationship(back_populates="bracket")