fix(isomp4): fix M4A moov-at-end probe failures and streaming fallback (#757)

* fix(stream): defer M4A probe until moov tail or fast-start prefix

Ranged moov-at-end M4A started Symphonia format probe as soon as ~384 KiB
linear data arrived, before the parallel tail prefetch filled the moov
atom — probe hit end of stream and skipped the track. Wait for tail_ready
or detect fast-start moov in the prefix; do not arm playback from linear
bytes alone when tail prefetch is active.

* fix(isomp4): skip EOF-spanning mdat after moov-at-end is parsed

Second-pass header scan with moov already loaded still tried to read
through mdat→EOF on RangedHttpSource holes, causing format probe
end of stream. Re-check play generation after moov wait.

* fix(isomp4): fix AtomIterator overread after seek in patched demuxer

`AtomIterator::new_root(reader, len)` treats `len` as bytes available
from the current `reader.pos()`, not the absolute file length. After
`mss.seek(resume_at)` we were passing the absolute `total_len`, so the
iterator thought there were `total_len` bytes left and tried to read
past EOF on the next iteration, returning "end of stream".

Fix: pass `total_len.map(|tl| tl.saturating_sub(resume_at))` (remaining
bytes from the new position) in both branches:
- `moov.is_none()` (moov-at-end layout, seek to moov offset)
- `moov.is_some()` (fast-start layout, skip bounded mdat body)

This caused Symphonia to fail probing moov-at-end M4A files read from
local disk (hot-cache) and from in-memory buffers — every decode attempt
returned "end of stream", analysis fell back to `byte_envelope_no_ebu`
(no EBU R128 loudness), and rodio produced distorted audio.

Also in this commit:
- `resolve_playback_format_hint()` helper to resolve hint from URL,
  stream suffix, Content-Disposition, or byte sniff
- ISO-BMFF diagnostic helpers (`isobmff_buffer_looks_complete`,
  `log_isobmff_buffer_diagnostic`, `mp4_suspect_zero_holes`)
- Probe-fallback path for ranged-stream failures now uses these helpers
  to decide whether to refetch or wait for the in-flight download

* chore(audio): remove redundant hint recomputation and add missing blank line

`bytes_hint_for_wait` in the ranged-stream fallback path was an exact
duplicate of `effective_hint` already in scope — reuse the existing binding.
Also add missing blank line after `wait_for_ranged_mp4_probe_ready` in mod.rs.

* chore(release): CHANGELOG and credits for PR #757

Add Fixed entry for M4A moov-at-end probe fix and credits line in
settingsCredits.ts under existing cucadmuh contributions.

* fix(audio): extract BuildSourceArgs to fix clippy::too_many_arguments

`build_playback_source_with_probe_fallback` had 12 parameters, exceeding
the clippy limit of 7. Group url/gen/hints/fade/hi-res/duration into
`BuildSourceArgs` so the function signature stays at 4 arguments.

src-tauri/crates/psysonic-audio/src/stream/mod.rs

@@ -17,6 +17,10 @@ mod ranged_http;
 mod reader;
 mod track_stream;
 
+pub(crate) use mp4::{
+    container_hint_is_mp4, isobmff_buffer_looks_complete, log_isobmff_buffer_diagnostic,
+    mp4_needs_tail_prefetch, mp4_suspect_zero_holes,
+};
 pub(crate) use local_file::LocalFileSource;
 pub(crate) use radio::{RadioLiveState, RadioSharedFlags, radio_download_task};
 pub(crate) use ranged_http::{RangedHttpSource, ranged_download_task};
@@ -65,5 +69,56 @@ pub(crate) fn maybe_arm_stream_playback(downloaded: u64, playback_armed: &std::s
         );
     }
 }
+
+/// Held until `RangedHttpSource` has moov metadata for Symphonia probe (tail prefetch
+/// or fast-start moov in the linear prefix).
+pub(crate) struct RangedMp4ProbeGate {
+    pub(crate) tail_ready: std::sync::Arc<std::sync::atomic::AtomicBool>,
+    pub(crate) buf: std::sync::Arc<std::sync::Mutex<Vec<u8>>>,
+    pub(crate) downloaded_to: std::sync::Arc<std::sync::atomic::AtomicUsize>,
+    pub(crate) gen_arc: std::sync::Arc<std::sync::atomic::AtomicU64>,
+    pub(crate) gen: u64,
+    pub(crate) format_hint: Option<String>,
+}
+
+/// Block until moov is reachable: tail prefetch completed or moov already in the
+/// downloaded prefix (fast-start). Avoids Symphonia probing moov-at-end M4A before
+/// the tail range is filled (format probe failed: end of stream).
+pub(crate) async fn wait_for_ranged_mp4_probe_ready(gate: &RangedMp4ProbeGate) -> Result<(), String> {
+    use std::sync::atomic::Ordering;
+    use std::time::{Duration, Instant};
+
+    const PREFIX_SCAN_MIN: usize = 64 * 1024;
+    let deadline = Instant::now() + Duration::from_secs(TRACK_READ_TIMEOUT_SECS);
+
+    loop {
+        if gate.gen_arc.load(Ordering::SeqCst) != gate.gen {
+            return Err("ranged-stream: superseded before moov metadata ready".into());
+        }
+        if gate.tail_ready.load(Ordering::Relaxed) {
+            crate::app_deprintln!("[stream] ranged: moov metadata ready (tail prefetch)");
+            return Ok(());
+        }
+        let dl = gate.downloaded_to.load(Ordering::Relaxed);
+        if dl >= PREFIX_SCAN_MIN {
+            let guard = gate.buf.lock().unwrap();
+            let n = dl.min(guard.len());
+            if !mp4::mp4_needs_tail_prefetch(&guard[..n], gate.format_hint.as_deref()) {
+                crate::app_deprintln!(
+                    "[stream] ranged: moov metadata ready (fast-start, {} KiB prefix)",
+                    n / 1024
+                );
+                return Ok(());
+            }
+        }
+        if Instant::now() >= deadline {
+            return Err(
+                "ranged-stream: timed out waiting for moov metadata (tail prefetch)".into(),
+            );
+        }
+        tokio::time::sleep(Duration::from_millis(20)).await;
+    }
+}
+
 /// Sleep interval when ring buffer is empty (prevents CPU spin).
 pub(crate) const RADIO_YIELD_MS: u64 = 2;