aictrl MCP: Add task dependency update tool

Problem

The aictrl MCP server currently lacks a tool to update task dependencies after a task has been created.

• create_task accepts a depends_on parameter, but there's no way to modify dependencies on existing tasks
• This makes it impossible to set up dependency relationships between tasks that were created in parallel or when task IDs weren't known at creation time

Use Case

When planning an epic with multiple stories/tasks:

1. Tasks are often created in parallel (for efficiency)
2. Task IDs aren't known until after creation
3. Need to set dependencies like "Story 1 blocks Stories 2-6" after all tasks exist

Proposed Solution

Add an update_task or set_task_dependencies MCP tool that accepts:

• task_id: The task to update
• depends_on: Array of task IDs this task depends on (replaces existing)
• Or: add_depends_on / remove_depends_on for incremental updates

Workaround

Currently, dependencies must be specified at task creation time, requiring sequential task creation rather than parallel.