mecatui: migrate /reflections proposal browsing to bounded controls #2174

Scope

Evaluate and migrate the /reflections proposal list and read-only proposal detail in cmd/mecatui/ui/reflections.go as separate bounded browsing regions. The list uses a height-8 cursor-centered window; detail increments detailScroll and only clamps a local value at render time (height-6, minimum four lines). This is distinct from the completed saved-memory browser.

Required outcome

• Use bounded.List for proposal selection and bounded.Viewport for proposal detail if their measured geometry and interaction boundaries fit; preserve the original list and detail behavior if a concrete region needs its specialized window. Keep titles, footer, range wording, and approval/rejection actions surface-owned. Use presentListRow for standard selected rows.
• Bound persisted detail offset and physical-row layout so Up after excessive Down/PageDown moves immediately; handle resize, long/multiline proposal evidence, compact heights, and safe untrusted text.
• Preserve proposal IDs/selection across paging/refresh, action eligibility, and existing request/response correlation.

Verification

Scenario-first tests for cursor reveal with many proposals, long detail with over-scroll and resize, optional action states, safe multiline text, and the correct proposal acted upon after refresh. Run focused UI and bounded tests.

Relates to #1742 and #1589.