Wire Node installer to read task slugs from tasks.json

[derek-palmer]

Parent

#45 (Deepen task metadata behind a Task Registry)

What to build

bin/install.js has its own hardcoded TASK_SKILL_SLUGS array that mirrors the Python installer's list. After #45 lands, src/codeforerunner/tasks.json is the source of truth for installable slugs. Wire the Node installer to read that JSON at install time instead of maintaining a duplicate hardcoded list.

Acceptance criteria

• bin/install.js reads tasks.json for skill slugs instead of the hardcoded TASK_SKILL_SLUGS array
• Node installer produces the same slug list as tasks.installable_slugs() from the Python side
• Existing Node installer behaviour is unchanged (same skills installed, same destinations)

Blocked by

• Deepen task metadata behind a Task Registry #45 (tasks.json must exist first)