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>

test/acceptance/scenario_coverage_test.go

@@ -25,6 +25,14 @@ import (
 // fails if a scenario is unmapped, a mapped test is missing, or an entry no
 // longer matches a real non-pending scenario.
 var scenarioCoverage = map[string]string{
+	// inline_expand.feature (ADR-031, #16)
+	"A summarized card expands to the full summary in place":      "TestExpandReturnsSummaryBodyFragment",
+	"An expanded card collapses back to the compact card":         "TestCollapseReturnsCompactCard",
+	"The expanded card offers the Q&A dock":                       "TestExpandedCardOffersChatDock",
+	"Only a summarized card offers expand":                        "TestCompactCardExpandOnlyWhenSummarized",
+	"With JS off the card still reaches the full summary":         "TestCompactCardHasNoJSDetailFallback",
+	"The detail page and the expanded card show the same summary": "TestDetailAndExpandShareSummaryBody",
+
 	// observability.feature (ADR-030, #15)
 	"Summarization latency is recorded per endpoint":            "TestSummarizerRecordsMetric",
 	"A failing summarizer endpoint records its failure outcome": "TestObserveSummarizeRecordsFailureOutcomes",