[P2][SHOP-02] Custom shopping UI, comparison and monitors

Programme: #1
Epic: #27

## Objective
Deliver the flagship user-owned shopping experience: exact source-backed offers rendered in a persistent custom comparison UI with explainable ranking and freshness monitoring.

## Scope
- Goal constraints such as budget, specs, condition, warranty, seller requirements and delivery deadline.
- Card/table comparison views backed by SHOP-01 offers and RES-02 claim/ranking logic.
- User-editable columns, filters, exclusions, pinned products and saved layouts.
- Explain why each result matches/fails constraints and which facts are missing.
- Freshness badges and selective refresh of affected offers/rankings.
- Price/availability monitoring through AUTO-01.
- Affiliate/commercial-conflict disclosure separated from ranking logic.
- Original/evidence navigation per offer/claim.

## Product rules
- Comparison remains directly usable without an active chat/model call.
- User ranking controls beat engagement/affiliate optimization.
- A missing fact must remain missing, not inferred as favorable.

## Acceptance criteria
- [ ] User can create/save/reopen a comparison and sort/filter it with inference disabled.
- [ ] Every critical field shows source/freshness or explicit unknown state.
- [ ] Source changes refresh only affected ranking/comparison dependencies.
- [ ] Ranking explanation reflects explicit user constraints and disclosed conflicts.
- [ ] Alerts are based on refreshed source state, not stale cached values.
- [ ] Original listings and evidence are reachable from the comparison.

## Dependencies
- SHOP-01
- UI-02
- AUTO-01

**First phase:** P2
**Maturity target:** P5
**Owner:** connectors-domains

Start by reading the dependency issues SHOP-01, UI-02, and AUTO-01 to understand the required offers, UI, and monitoring inputs. Use the acceptance criteria as the definition of done: saved comparisons, source and freshness states, affected-only refresh, explainable ranking, alerts from refreshed data, and reachable original evidence.

Written by the indexing model from the issue text.