feat(podcasts): web UI — /podcasts page, feed detail, download lifecycle (task 1.9)

Rendering ownership holds throughout: every piece of server data is
templ-rendered; htmx swaps partials; the only TS is the Add-Feed modal
toggle + error surfacing (pure client-local state, bundled via
web/src/podcasts.ts with automatic bundle-hash stamping).

Sidebar: /podcasts nav entry (D13, between Series and Collections),
gated by a ShowPodcastsNav flag resolved centrally in
getTemplateUserWithTheme (one indexed COUNT — same class of
per-request lookup as the live-user guard). New 'podcast' icon.

/podcasts: header + Add Feed modal (htmx post → HX-Redirect to the
feed page; inline error surfacing on failure), subscription-scoped
search + facet bar (host/tag/language — server-side GET filters, no
JS), grid cards with download counts / new-episodes / complete /
explicit badges. Empty states for no-library (admin creates it first)
and no-subscriptions.

Feed detail: hero (artwork, host/publisher, tags, fetch state), action
row — Download All, Refresh, ORDER SELECTOR (D5 override), serial
one-click oldest-first suggestion (never silent), auto-download policy
select (D6), Unsubscribe (files retained), admin Remove Feed — gap
banner (D8 count), and the EPISODE LIST with the full lifecycle inline
(D8/D19): pending greyed + Download button (every non-downloaded
episode has one), queued/downloading pulse, failed RED + reason text +
Retry (same endpoint). The list is a self-refreshing partial: re-fetch
on the podcast:changed HX-Trigger and polls every 4s ONLY while the
server says downloads are active (it renders the polling variant).

API endpoints grew HX awareness: 204 + HX-Trigger podcast:changed (or
HX-Redirect for add/unsubscribe/remove) — the sanctioned Go-handler
response channels; JSON callers keep JSON. AddFeed result exposes the
fetch-error text for the redirect.

Dates render in the requesting user's timezone (D17) via
utils.FormatTimeInTimezone; episodes play through the existing
/readers/{id} audio reader (episodes ARE audiobook items — no new
player code day one). CSP tripwire (templates/csp_source_test.go)
passes: no inline scripts, no on*= handlers, no hx-on/js: vals.

templates/header.templ

@@ -70,6 +70,12 @@ templ Header(user User, currentPath string) {
 					@Icon("layers", "h-5 w-5 shrink-0")
 					<span>Series</span>
 				</a>
+				if user.ShowPodcastsNav {
+					<a href="/podcasts" class={ activeClass(currentPath, "/podcasts") }>
+						@Icon("podcast", "h-5 w-5 shrink-0")
+						<span>Podcasts</span>
+					</a>
+				}
 				<a href="/collections" class={ activeClass(currentPath, "/collections") }>
 					@Icon("folder", "h-5 w-5 shrink-0")
 					<span>Collections</span>