feat(deck-builder): Wincon tag ↔ win-condition engine cross-link (E125)

[georgepapagapitos]

Summary

• User-tagged Wincon cards now surface in the Power tab's Win Conditions panel, and engine-detected win-condition cards offer a "tag as Wincon" affordance — the two directions from E125's board spec.
• Display-level only: detectWinConditions (frontend/src/deck-builder/services/winConditions/detect.ts) is untouched, still pure, no new inputs — no v2-wincon signature bump needed.
• New Deck.winConTags?: string[] — a narrow, single-purpose field (card names only, no goals/colors/categories), explicitly NOT a reopening of the general card-tag system retired in feat(deck): retire user card tags — automatic role pills take over the filter lens #1134. Set only via a user-confirmed click on an evidence chip's tag toggle.
• Dedupe rule: a card that's both engine evidence and user-tagged shows the mark on its existing row (accent-filled tag icon, aria-pressed); a tag the engine doesn't currently surface gets a separate dashed "Tagged by you" section, so a tag never disappears silently when the live analysis changes.

Files touched

• frontend/src/deck-builder/services/winConditions/winConTags.ts (+test) — new pure module: tagOnlyWinCons (merge/dedupe) and toggleWinConTag (add/remove).
• frontend/src/components/deck/WinConditionPanel.tsx (+test) — per-evidence-chip tag toggle (WinConEvidenceItem), the "Tagged by you" section, restructured render so the tag section survives the noClearWinCondition empty state.
• frontend/src/components/deck/WinConditionPanel.css — toggle button styles (aria-pressed accent fill, 44px coarse-pointer target, reduced-motion guard), dashed border for the tagged-only section.
• frontend/src/store/decks.ts — new Deck.winConTags?: string[] field, additive/whole-row-synced like primer.
• frontend/src/pages/DeckEditorPage.tsx — wires winConTags/onToggleWinConTag into the existing WinConditionPanel call site via updateDeck (same pattern as bracketOverride/archetypeOverride).

Test plan

• winConTags.test.ts — 11 cases: tagOnlyWinCons (primary/secondary dedupe, no-clear-wincon still surfaces tags, mixed split, de-dupe/order) + toggleWinConTag (add/remove/no-mutate).
• WinConditionPanel.test.tsx — 7 cases covering engine-only / tag-only / both / none states, dedupe, live toggle click, read-only mode when the callback is omitted.
• npm run typecheck / lint / format:check / test (both packages) — all green; coverage gate enforced (dev Postgres up).
• Browser validation against the dev account's seeded "Krenko" commander deck (real UI click for the tag toggle; realistic seeded winConditions for the other 3 states, since the live EDHREC/Scryfall analysis pipeline was rate-limited in this environment) — 320/360(dpr3)/600/768/1024/1440, light+dark at 360+1440. polish:responsive-audit run — no findings.
• Dev account cleanup — Krenko deck restored to its exact original state (verified byte-identical) after validation.