Step 7.5b1: cspot (philippe44 fork) builds and links on the P4

- external/cspot: git submodule, pinned to philippe44/cspot 3010349
  (bell ed2d6e9); GPL-3.0.
- components/spotify: project component wrapping cspot. bell trimmed to
  what cspot needs (Tremor Vorbis; no codec wrapper, sinks, MQTT, web
  server, fmt, regex; cJSON from IDF). Xtensa biquad assembly filtered
  out (P4 is RISC-V). CMAKE_POLICY_VERSION_MINIMUM 3.5 for CMake 4.
- Patches in components/spotify/patches, applied at configure time:
  nanopb generator works with protobuf >= 5 (MakeClass removed);
  URLParser.cpp missing <cstdio>/<cstring> for GCC 14.
- CONFIG_COMPILER_CXX_EXCEPTIONS=y (cspot needs exceptions).
- spotify_init() only builds a LoginBlob (link check).
- CLAUDE.md: submodule init and IDF-venv Python packages for nanopb.
- Verified on board: "cspot linked: device "P4 AES67", zeroconf info 588
  bytes"; HLS still playing, PTP locked; image 1.83 MB (70% free).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main/player.c

@@ -8,6 +8,7 @@
 #include "audio_ring.h"
 #include "decoder.h"
 #include "hls.h"
+#include "spotify.h"
 #include "esp_log.h"
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
@@ -118,7 +119,10 @@ esp_err_t player_init(void)
     if (err != ESP_OK) {
         return err;
     }
-    err = hls_start(decoder_feed);
+    cJSON *sc = cfg_get("source");
+    spotify_init(cJSON_GetObjectItemCaseSensitive(sc, "spotify_name")->valuestring);
+    cJSON_Delete(sc);
+        err = hls_start(decoder_feed);
     if (err != ESP_OK) {
         return err;
     }