Exclude idea items from planner and ready backlog flows

[trsdn]

Problem

Idea items are still able to leak into the wrong workflow.

A concrete symptom is that an item marked like an idea can still end up with labels such as status:blocked and needs:stakeholder-decision, which suggests it was touched by planner/runtime paths that should not treat it as ready backlog work.

That breaks the intended separation between idea intake and executable sprint work.

Desired behavior

Idea items must be modeled and filtered consistently so they never enter the normal ready/planning flow unless they are explicitly converted out of the idea state.

Whether the canonical representation remains type:idea or changes to something like status:idea, the behavior must be consistent and enforced.

Acceptance criteria

• Define the canonical way to represent idea items (type:idea vs another status-based model) and document it.
• Sprint planning eligibility excludes idea items completely.
• Ready backlog views exclude idea items completely.
• Idea items are not relabeled into execution-oriented states by planner/runtime flows unless they are intentionally converted.
• If idea items need a separate conversion step before refinement/planning, that rule is explicit.
• Regression coverage is added for planner eligibility and dashboard/backlog filtering of idea items.