feat: Add task-mcp server for task management via MCP

Implements 10 MCP tools for task management:
- CRUD: task_add, task_list, task_show, task_close, task_update
- Search: task_similar (pgvector), task_context
- Relations: task_link, task_checklist_add, task_checklist_toggle

Uses PostgreSQL with pgvector for semantic search via LiteLLM embeddings.
Connects via SSH tunnel to docker-host:5435.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/tools/relations.ts

@@ -0,0 +1,81 @@
+// Task relations: dependencies and checklists
+
+import { query, queryOne, execute } from '../db.js';
+
+interface TaskLinkArgs {
+  from_id: string;
+  to_id: string;
+  link_type: string;
+}
+
+interface ChecklistAddArgs {
+  task_id: string;
+  item: string;
+}
+
+interface ChecklistToggleArgs {
+  item_id: number;
+  checked: boolean;
+}
+
+/**
+ * Create a dependency between tasks
+ */
+export async function taskLink(args: TaskLinkArgs): Promise<string> {
+  const { from_id, to_id, link_type } = args;
+
+  try {
+    await execute(
+      `INSERT INTO task_links (from_task_id, to_task_id, link_type)
+       VALUES ($1, $2, $3)
+       ON CONFLICT (from_task_id, to_task_id, link_type) DO NOTHING`,
+      [from_id, to_id, link_type]
+    );
+
+    return `Linked: ${from_id} ${link_type} ${to_id}`;
+  } catch (error) {
+    return `Error creating link: ${error}`;
+  }
+}
+
+/**
+ * Add a checklist item to a task
+ */
+export async function checklistAdd(args: ChecklistAddArgs): Promise<string> {
+  const { task_id, item } = args;
+
+  // Get next position
+  const result = await queryOne<{ max: number }>(
+    `SELECT COALESCE(MAX(position), 0) + 1 as max
+     FROM task_checklist WHERE task_id = $1`,
+    [task_id]
+  );
+
+  const position = result?.max || 1;
+
+  await execute(
+    `INSERT INTO task_checklist (task_id, item, position)
+     VALUES ($1, $2, $3)`,
+    [task_id, item, position]
+  );
+
+  return `Added to ${task_id}: ${item}`;
+}
+
+/**
+ * Toggle a checklist item
+ */
+export async function checklistToggle(args: ChecklistToggleArgs): Promise<string> {
+  const { item_id, checked } = args;
+
+  const result = await execute(
+    `UPDATE task_checklist SET checked = $1 WHERE id = $2`,
+    [checked, item_id]
+  );
+
+  if (result === 0) {
+    return `Checklist item not found: ${item_id}`;
+  }
+
+  return `${checked ? 'Checked' : 'Unchecked'}: item #${item_id}`;
+}