feat: KB Accelerator — convert KB articles into interactive flows

Full-stack implementation of the KB Accelerator feature that converts
static MSP knowledge base articles into interactive troubleshooting
and procedural flows using AI.

Backend:
- Migrations 054/055: kb_imports, kb_import_nodes tables + plan_limits KB columns
- SQLAlchemy models with relationships and self-referential node hierarchy
- Text extraction service (txt, paste, docx with structural metadata)
- AI conversion service with MSP-specialist prompts for both flow types
- 8 API endpoints: upload, get, list, convert, edit node, commit, delete, quota
- Tier-gated access via plan_limits (free: 3 lifetime, pro/team: unlimited)
- 8 integration tests covering upload, get/list, quota, commit, delete

Frontend:
- TypeScript types and API client for all KB Accelerator endpoints
- Multi-step wizard page: upload → processing → review → success
- Upload screen with paste/file tabs, drag-drop, target type selector
- Two-panel review screen with source highlighting and node cards
- Per-node actions: approve, edit, regenerate, insert, delete
- Confidence color indicators (green/amber/red)
- Sidebar navigation with Sparkles icon
- Code-split lazy-loaded route at /kb-accelerator

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

backend/alembic/versions/054_add_kb_imports.py

@@ -0,0 +1,79 @@
+"""add kb_imports and kb_import_nodes tables
+
+Revision ID: 054
+Revises: 053
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+revision = "054"
+down_revision = "053"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_table(
+        "kb_imports",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True, server_default=sa.text("gen_random_uuid()")),
+        sa.Column("account_id", UUID(as_uuid=True), sa.ForeignKey("accounts.id", ondelete="CASCADE"), nullable=False, index=True),
+        sa.Column("created_by", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True),
+        sa.Column("source_filename", sa.String(500), nullable=True),
+        sa.Column("source_format", sa.String(20), nullable=False),
+        sa.Column("source_text", sa.Text, nullable=False),
+        sa.Column("source_metadata", JSONB, nullable=True),
+        sa.Column("target_type", sa.String(20), nullable=False),
+        sa.Column("status", sa.String(20), nullable=False, server_default="processing"),
+        sa.Column("confidence_avg", sa.Float, nullable=True),
+        sa.Column("error_message", sa.Text, nullable=True),
+        sa.Column("processing_time_ms", sa.Integer, nullable=True),
+        sa.Column("ai_tokens_input", sa.Integer, nullable=True),
+        sa.Column("ai_tokens_output", sa.Integer, nullable=True),
+        sa.Column("tree_id", UUID(as_uuid=True), sa.ForeignKey("trees.id", ondelete="SET NULL"), nullable=True),
+        sa.Column("batch_id", UUID(as_uuid=True), nullable=True, index=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.text("now()")),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.text("now()")),
+        sa.CheckConstraint(
+            "source_format IN ('txt', 'paste', 'docx', 'pdf', 'html', 'md')",
+            name="ck_kb_imports_source_format",
+        ),
+        sa.CheckConstraint(
+            "target_type IN ('troubleshooting', 'procedural')",
+            name="ck_kb_imports_target_type",
+        ),
+        sa.CheckConstraint(
+            "status IN ('processing', 'ready', 'committed', 'failed')",
+            name="ck_kb_imports_status",
+        ),
+    )
+
+    op.create_index("ix_kb_imports_status", "kb_imports", ["status"])
+    op.create_index("ix_kb_imports_created_at_desc", "kb_imports", [sa.text("created_at DESC")])
+
+    op.create_table(
+        "kb_import_nodes",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True, server_default=sa.text("gen_random_uuid()")),
+        sa.Column("kb_import_id", UUID(as_uuid=True), sa.ForeignKey("kb_imports.id", ondelete="CASCADE"), nullable=False, index=True),
+        sa.Column("node_order", sa.Integer, nullable=False),
+        sa.Column("node_type", sa.String(20), nullable=False),
+        sa.Column("content", JSONB, nullable=False),
+        sa.Column("parent_node_id", UUID(as_uuid=True), sa.ForeignKey("kb_import_nodes.id", ondelete="SET NULL"), nullable=True),
+        sa.Column("source_excerpt", sa.Text, nullable=True),
+        sa.Column("confidence_score", sa.Float, nullable=False),
+        sa.Column("user_edited", sa.Boolean, nullable=False, server_default=sa.text("false")),
+        sa.Column("user_approved", sa.Boolean, nullable=False, server_default=sa.text("false")),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.text("now()")),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.text("now()")),
+        sa.CheckConstraint(
+            "node_type IN ('question', 'resolution', 'step', 'section_header', 'warning', 'action')",
+            name="ck_kb_import_nodes_node_type",
+        ),
+    )
+
+    op.create_index("ix_kb_import_nodes_confidence", "kb_import_nodes", ["confidence_score"])
+
+
+def downgrade():
+    op.drop_table("kb_import_nodes")
+    op.drop_table("kb_imports")