feat(web): inline-expand summary + Q&A in the list (ADR-031, #16)

Click a summarized card → its full summary (summaryBody) + chat dock (chatReveal)
expand in place via HTMX (GET /v/{id}/expand → expandedCard), collapse back via
GET /v/{id}/card → compact VideoCard. Same <li id>, outerHTML swap — the existing
list-fragment pattern. The card title carries href=/v/{id} as the no-JS fallback
(detail page stays for no-JS + deep links); only summarized cards expand. Reuses
summaryBody + chatReveal so the expanded card never drifts from the detail page.

BDD: inline_expand.feature un-pended + mapped. TDD: 6 handler/fragment tests
(expand/collapse fragments, chat dock, summarized-only, no-JS href, shared body).
Minimal CSS only — the TUI/charm restyle is #17.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/web/handlers.go

@@ -151,6 +151,8 @@ func (a *App) Router() http.Handler {
 	app := http.NewServeMux()
 	app.HandleFunc("GET /{$}", a.handleList)
 	app.HandleFunc("GET /v/{videoId}", a.handleDetail)
+	app.HandleFunc("GET /v/{videoId}/expand", a.handleExpand)
+	app.HandleFunc("GET /v/{videoId}/card", a.handleCard)
 	app.HandleFunc("POST /v/{videoId}/action", a.handleAction)
 	app.HandleFunc("POST /v/{videoId}/summarize", a.handleRequestSummarize)
 	app.HandleFunc("POST /v/{videoId}/retry-now", a.handleRetryNow)
@@ -283,6 +285,48 @@ func (a *App) handleDetail(w http.ResponseWriter, r *http.Request) {
 	a.render(w, r, DetailPage(*row, a.Chat != nil))
 }
 
+// handleExpand returns the inline-expanded card fragment — the full summary +
+// chat dock swapped into the list card in place (ADR-031). Only summarized videos
+// have a summary to expand; a non-summarized id is a 404 (the compact card never
+// offers expand for it).
+func (a *App) handleExpand(w http.ResponseWriter, r *http.Request) {
+	userID, ok := a.currentUserID(w, r)
+	if !ok {
+		return
+	}
+	videoID := r.PathValue("videoId")
+	row, err := a.Store.GetSummaryByVideo(r.Context(), userID, videoID)
+	if errors.Is(err, store.ErrNotFound) {
+		http.NotFound(w, r)
+		return
+	}
+	if err != nil {
+		a.serverError(w, r, "get summary", err)
+		return
+	}
+	a.render(w, r, expandedCard(*row, a.Chat != nil))
+}
+
+// handleCard returns the compact card fragment — the collapse target that returns
+// an expanded card to its compact form in the list (ADR-031).
+func (a *App) handleCard(w http.ResponseWriter, r *http.Request) {
+	userID, ok := a.currentUserID(w, r)
+	if !ok {
+		return
+	}
+	videoID := r.PathValue("videoId")
+	row, err := a.Store.GetVideoRow(r.Context(), userID, videoID)
+	if errors.Is(err, store.ErrNotFound) {
+		http.NotFound(w, r)
+		return
+	}
+	if err != nil {
+		a.serverError(w, r, "get video", err)
+		return
+	}
+	a.render(w, r, VideoCard(*row))
+}
+
 // handleAction toggles one action: re-clicking an active verb clears it, else it
 // is set (the store enforces watched↔skipped exclusion atomically). It returns
 // the refreshed button-group fragment for HTMX; without JS it redirects back to