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/app/schemas/kb_accelerator.py

@@ -0,0 +1,142 @@
+"""Pydantic schemas for KB Accelerator."""
+from typing import Any, Literal, Optional
+from uuid import UUID
+
+from pydantic import BaseModel, Field
+
+
+# ── Requests ──
+
+
+class KBUploadTextRequest(BaseModel):
+    """Upload KB article via text paste."""
+
+    content: str = Field(..., min_length=10, max_length=500_000)
+    title: Optional[str] = Field(None, min_length=1, max_length=255)
+    target_type: Optional[Literal["troubleshooting", "procedural"]] = Field(
+        None, description="Target flow type. If omitted, AI decides."
+    )
+
+
+class KBNodeEditRequest(BaseModel):
+    """Edit a specific KB import node during review."""
+
+    operation: Literal[
+        "approve", "reject", "edit", "delete", "regenerate", "insert_after"
+    ]
+    content: Optional[dict[str, Any]] = Field(
+        None, description="Updated node content (required for 'edit' and 'insert_after')"
+    )
+    guidance: Optional[str] = Field(
+        None,
+        max_length=2000,
+        description="User guidance for 'regenerate' operation",
+    )
+
+
+class KBCommitRequest(BaseModel):
+    """Optional overrides when committing a KB import to the flow library."""
+
+    name: Optional[str] = Field(None, min_length=1, max_length=255)
+    description: Optional[str] = Field(None, max_length=2000)
+    category_id: Optional[UUID] = None
+
+
+# ── Responses ──
+
+
+class KBImportNodeResponse(BaseModel):
+    """A single generated node in a KB import."""
+
+    id: UUID
+    kb_import_id: UUID
+    node_order: int
+    node_type: str
+    content: dict[str, Any]
+    parent_node_id: Optional[UUID] = None
+    source_excerpt: Optional[str] = None
+    confidence_score: float
+    user_edited: bool
+    user_approved: bool
+
+    model_config = {"from_attributes": True}
+
+
+class KBUploadResponse(BaseModel):
+    """Response after uploading a KB article."""
+
+    id: UUID
+    status: str
+    source_format: str
+
+
+class KBImportResponse(BaseModel):
+    """Full KB import detail with nodes."""
+
+    id: UUID
+    account_id: UUID
+    created_by: UUID
+    source_filename: Optional[str] = None
+    source_format: str
+    source_text: str
+    source_metadata: Optional[dict[str, Any]] = None
+    target_type: str
+    status: str
+    confidence_avg: Optional[float] = None
+    error_message: Optional[str] = None
+    processing_time_ms: Optional[int] = None
+    ai_tokens_input: Optional[int] = None
+    ai_tokens_output: Optional[int] = None
+    tree_id: Optional[UUID] = None
+    nodes: list[KBImportNodeResponse] = []
+    created_at: str
+    updated_at: str
+
+    model_config = {"from_attributes": True}
+
+
+class KBImportSummary(BaseModel):
+    """Lightweight import item for list view."""
+
+    id: UUID
+    source_filename: Optional[str] = None
+    source_format: str
+    target_type: str
+    status: str
+    confidence_avg: Optional[float] = None
+    node_count: int = 0
+    created_at: str
+
+    model_config = {"from_attributes": True}
+
+
+class KBImportListResponse(BaseModel):
+    """Paginated list of KB imports."""
+
+    items: list[KBImportSummary]
+    total: int
+    skip: int
+    limit: int
+
+
+class KBCommitResponse(BaseModel):
+    """Response after committing a KB import to the flow library."""
+
+    tree_id: UUID
+    import_id: UUID
+    tree_type: str
+
+
+class KBQuotaResponse(BaseModel):
+    """Current KB Accelerator entitlements and usage for the user's account."""
+
+    plan: str
+    kb_accelerator_enabled: bool
+    lifetime_conversions_used: int
+    lifetime_conversions_limit: Optional[int] = None
+    allowed_formats: list[str]
+    detailed_analysis: bool
+    conversational_refinement: bool
+    step_library_matching: bool
+    history_limit: Optional[int] = None
+    can_convert: bool