Add task priority enum and rename priority to rank

[SachaProbo]

Rename the existing integer priority field to rank across the entire stack (DB, Go, GraphQL, MCP, frontend) since it represents positional ordering within a state, not semantic importance.

Add a new priority field with enum values URGENT, HIGH, MEDIUM, LOW exposed through all three API surfaces (GraphQL, MCP, CLI) with validation, create/update support, and a migration that defaults existing rows to MEDIUM.

Update PriorityLevel component to accept the priority enum directly: LOW/MEDIUM/HIGH show 1/2/3 bars, URGENT shows a bang (!) icon. Add priority selector with icons to the task create/edit form dialog.

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Summary by cubic

Renamed the integer task priority to rank (positional order) and introduced a new priority enum (URGENT/HIGH/MEDIUM/LOW) across DB, services, and APIs. Updated the console with a priority selector and icons; migration defaults existing tasks to MEDIUM.

• New Features

  • Added TaskPriority enum to GraphQL/MCP/CLI with validation and create/update support.
  • Updated @probo/ui PriorityLevel to accept the enum; LOW/MEDIUM/HIGH render 1/2/3 bars and URGENT shows a bang; added a priority selector to the task form.

• Migration

  • Run the SQL migration to rename column priority→rank and add the task_priority enum.
  • Breaking changes: Task.priority is now an enum; new Task.rank (Int) holds position; TaskOrderField.RANK replaces PRIORITY.
  • Update clients to send priority on create, use rank to reorder, and order queries by RANK.

^{Written for commit 52a46c5. Summary will update on new commits.}

[cubic-dev-ai]

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