Port anchor-based sidebar reordering to durable review history

[lynnswap]

Parent: #96
Related: #102

Contract

The recovery must preserve the independent post-v0.6.2 sidebar reorder correction without porting the generic Codex chat sidebar.

Drag/drop resolves a semantic anchor (beforeCWD / beforeReviewID), not a transient visible/store array index. The durable history transaction updates manual workspace/review order atomically.

Acceptance criteria

• Workspace groups and reviews reorder by stable before-anchor identity.
• Filtered/hidden rows, collapsed sections, grouped workspaces, blank-area drops, upward/downward moves, and moves to the full-order end produce the intended durable order.
• A no-op drop does not write or animate.
• Reorder survives app restart and history paging.
• A missing/stale anchor is a typed no-op/error according to the command boundary; no guessed array index.
• Workspace and review order update in one global history revision and preserve stable row identity/selection.
• Tests port the behavior from 1682c34 / PR Refactor sidebar reorder drops around anchors #50 without copying generic-chat/DataKit code.

Historical evidence

PR #50 (1682c347e87ebd0e3f417792c4c07bec334b9a79) changed index-based drops to anchor-based ordering immediately after v0.6.2.

[lynnswap]

Anchor semantics are fixed: missing moving ID or stale/wrong-scope non-nil anchor is a typed no-write error; nil anchor means canonical end; same-position move returns false with no revision; success returns true and commits exactly one global revision. Filters/groups supply stable IDs only and never translate visible indices into durable order.