mecatui: evaluate bounded MCP resource and prompt pickers #2175

Scope

Evaluate bounded selectable browsing for the MCP resource and prompt pickers in cmd/mecatui/ui/mcp.go. Each currently renders every advertised item and uses an index-only cursor; the surface's Render(width, height) discards offered height. With enough advertised items the picker can exceed the card and hide its selection. Treat resource and prompt lists separately from MCP status, resource preview, and prompt argument forms.

Required outcome

• Establish and test the constrained-geometry inconsistency for each picker; if justified, use bounded.List with stable server+resource URI or server+prompt name identities, measured chrome, selection reveal, standard presentListRow treatment, and surface-owned overflow/footers. Explicitly retain a region if migration offers no net benefit.
• Preserve sanitized labels, names/server attribution, resource read → preview → insert, prompt argument selection/fetch, capability/availability states, and the existing key/close/back contract. Do not add wheel/click semantics without a tested interaction decision; click-to-select is tracked in mecatui: click-to-select a row in the TUI picker/overlay lists (skills, models, agents, MCP, schedule, etc.) #769.

Verification

Scenario-first tests for numerous resources/prompts at narrow/short sizes, overflow, cursor/identity after refresh, and activation/preview/argument transitions. Run focused MCP/UI and bounded tests.

Relates to #1742 and #1589.