feat: beta feedback widget — frictionless in-session feedback

Full-stack beta feedback system:

Backend:
- BetaFeedback model with reaction, category, text, page context
- POST /feedback/beta (any auth user), GET /feedback/beta (admin, filtered)
- Alembic migration 065 with indexes on user_id, reaction, created_at

Frontend:
- Persistent "Feedback" tab on right edge of all authenticated pages
- Slide-out panel: quick reaction (👍😐👎), category pills, optional text
- Auto-captures page URL and FlowPilot session ID
- Hidden on mobile (<640px), closes on Escape/outside click
- Shows "Thanks!" confirmation then auto-closes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/alembic/versions/065_add_beta_feedback_table.py

@@ -0,0 +1,43 @@
+"""add beta_feedback table
+
+Revision ID: 065
+Revises: 064
+Create Date: 2026-03-23 00:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID
+
+
+# revision identifiers, used by Alembic.
+revision: str = "065"
+down_revision: Union[str, None] = "064"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "beta_feedback",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True),
+        sa.Column("user_id", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("reaction", sa.String(10), nullable=False),
+        sa.Column("category", sa.String(30), nullable=True),
+        sa.Column("text", sa.Text, nullable=True),
+        sa.Column("page_url", sa.String(500), nullable=True),
+        sa.Column("session_id", sa.String(100), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+    )
+    op.create_index("ix_beta_feedback_user_id", "beta_feedback", ["user_id"])
+    op.create_index("ix_beta_feedback_reaction", "beta_feedback", ["reaction"])
+    op.create_index("ix_beta_feedback_created_at", "beta_feedback", ["created_at"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_beta_feedback_created_at", table_name="beta_feedback")
+    op.drop_index("ix_beta_feedback_reaction", table_name="beta_feedback")
+    op.drop_index("ix_beta_feedback_user_id", table_name="beta_feedback")
+    op.drop_table("beta_feedback")