BE-PR-001: Rename Propose -> Proposal across backend

- New canonical model: Proposal, ProposalStatus (app/models/proposal.py)
- New canonical router: /projects/{id}/proposals (app/api/routers/proposals.py)
- Schemas renamed: ProposalCreate, ProposalUpdate, ProposalResponse, etc.
- Old propose.py and proposes.py kept as backward-compat shims
- Legacy /proposes API still works (delegates to /proposals handlers)
- DB table name (proposes), column (propose_code), and permission names
  (propose.*) kept unchanged for zero-migration compat
- Updated init_wizard.py comments

app/models/proposal.py

@@ -0,0 +1,34 @@
+from sqlalchemy import Column, Integer, String, Text, DateTime, ForeignKey, Enum
+from sqlalchemy.sql import func
+from app.core.config import Base
+import enum
+
+
+class ProposalStatus(str, enum.Enum):
+    OPEN = "open"
+    ACCEPTED = "accepted"
+    REJECTED = "rejected"
+
+
+class Proposal(Base):
+    __tablename__ = "proposes"  # keep DB table name for compat
+
+    id = Column(Integer, primary_key=True, index=True)
+    propose_code = Column(String(64), nullable=True, unique=True, index=True)  # keep column name for DB compat
+    title = Column(String(255), nullable=False)
+    description = Column(Text, nullable=True)
+    status = Column(Enum(ProposalStatus, values_callable=lambda x: [e.value for e in x]), default=ProposalStatus.OPEN)
+
+    project_id = Column(Integer, ForeignKey("projects.id"), nullable=False)
+    created_by_id = Column(Integer, ForeignKey("users.id"), nullable=True)
+
+    # Populated server-side after accept; links to the generated feature story task
+    feat_task_id = Column(String(64), nullable=True)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+
+# Backward-compatible aliases
+ProposeStatus = ProposalStatus
+Propose = Proposal