fix: align queue targets and deduplicate backlog items

[liorp]

Problem

plan queue defaults to a subjective target of 100 while next uses the configured target. A dimension at 90 with a target of 85 is consequently shown only by the plan command. The backlog also emits mechanical findings twice because objective and triage partitions overlap.

Change

Pass the configured target to the plan queue builder. Combine backlog partitions by work-item ID, preserving order and existing execution/triage classification.

Validation

• Three regressions cover duplicate mechanical findings, retained review/concern findings, and targets on both sides of an assessed score. Two failed before the fix.
• All 3,511 command, engine, plan and review tests pass. Ruff passes for changed files.
• Read-only verification against a real TypeScript monorepo state: 1,980 backlog rows with 1,980 unique IDs; both queue surfaces return the same nine items with the configured target.
• Independent review found no blockers. No scoring or resolution behavior is changed.
• Full upstream suite: 5,663 passed, 152 skipped, three Bash unused-source parser failures. Those same three failures reproduce with unchanged baseline source.