web: chapter audio player + render button

Chapter view now shows a narration card between title and prose
with three states:
  - succeeded → HTML5 <audio> + voice + duration + download link
  - running   → 'rendering…' banner with relative start time
  - none/failed → 'Render audio' POST button (spawns background
                  tokio task calling narrate::run)

ServeDir mounted at /audio serves WAVs from the f5-tts bind-mount
read-only. Range requests work, so 16-min chapters seek cleanly.

Deploy needs: compose mount /mnt/cache/appdata/f5-tts/audio:/audio:ro
on skald (already staged in /mnt/cache/appdata/skald/compose.yml on
Lucy).

Cargo.lock

@@ -803,6 +803,12 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "http-range-header"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9171a2ea8a68358193d15dd5d70c1c10a2afc3e7e4c5bc92bc9f025cebd7359c"
+
 [[package]]
 name = "httparse"
 version = "1.10.1"
@@ -1909,6 +1915,7 @@ dependencies = [
  "chrono",
  "clawdforge",
  "regex",
+ "reqwest",
  "serde",
  "serde_json",
  "sqlx",
@@ -2393,11 +2400,19 @@ checksum = "68d6fdd9f81c2819c9a8b0e0cd91660e7746a8e6ea2ba7c6b2b057985f6bcb51"
 dependencies = [
  "bitflags",
  "bytes",
+ "futures-core",
  "futures-util",
  "http",
  "http-body",
  "http-body-util",
+ "http-range-header",
+ "httpdate",
+ "mime",
+ "mime_guess",
+ "percent-encoding",
  "pin-project-lite",
+ "tokio",
+ "tokio-util",
  "tower",
  "tower-layer",
  "tower-service",