daemon: link daedalus-fourier + log substrate availability at startup

First incremental step toward H.264 daemon-rewrite (daedalus-v4l2#11):
make the daedalus-fourier kernel library available to the daemon
process so subsequent patches can substitute its primitives
(IDCT 4×4, IDCT 8×8, luma vertical deblock, etc.) for libavcodec's
per-MB pixel math.

This patch does NOT yet dispatch any kernels.  It only:

  - Adds `pkg_check_modules(DAEDALUS_FOURIER REQUIRED daedalus-fourier)`
    to the daemon's CMakeLists, with explicit link ordering
    (libdaedalus_core.a must precede -lvulkan because the static
    archive references vulkan symbols and the linker resolves
    left-to-right).  We bypass IMPORTED_TARGET because pkg-config's
    Requires.private chain leaves CMake's dependency graph reordering
    the archive after -lvulkan, breaking the static link.

  - Calls daedalus_ctx_create_no_qpu() at daemon startup, logs the
    substrate-availability line, destroys the context at exit.
    no_qpu mode skips V3D Vulkan probe — proves linkage works
    without depending on shader-path resolution (which is a
    separate piece of work, since v3d_runner currently loads
    .spv files from cwd-relative paths and consumer would need
    a search path override).

Sample journal line:

  [2026-05-21 17:59:35.271 INFO] daedalus-fourier: linked, ctx alive
  (no_qpu mode; has_qpu=0)

Build-test verified on hertz (Pi 5 dev host) against an installed
copy of daedalus-fourier r35+gd87239d (from marfrit/daedalus-fourier
PR #1).  Binary links cleanly, --help prints, daemon mode opens
chardev (fails predictably on hertz which has no daedalus_v4l2
kmod; on higgs this is the existing working path).

Follow-up patches per daedalus-v4l2#11:

  1. Instrument the existing libavcodec decode path to count
     per-frame IDCT blocks / deblock edges / MC tiles so we have
     a baseline of what work the daemon dispatches for a typical
     YouTube H.264 stream.
  2. Substitute daedalus-fourier kernels one at a time, measuring
     CPU saved per substitution.
  3. Wire shader path resolution into daedalus_ctx_create() for
     the QPU substrate (V3D opportunistic helper paths).

Wire protocol unchanged.  DAEDALUS_PROTO_VERSION stays at 0.

daemon/src/main.c

@@ -22,6 +22,8 @@
 
 #include <libavutil/log.h>
 
+#include <daedalus.h>
+
 static volatile sig_atomic_t g_terminate = 0;
 
 static void on_signal(int sig)
@@ -120,6 +122,26 @@ int main(int argc, char **argv)
 	/* Mute FFmpeg's own chattiness unless the user asked. */
 	fm.av_log_set_level(verbose ? AV_LOG_INFO : AV_LOG_WARNING);
 
+	/*
+	 * Initialise daedalus-fourier early so we can log substrate
+	 * availability up front.  daedalus_ctx_create_no_qpu() skips
+	 * the V3D Vulkan probe — we're not dispatching any kernels
+	 * yet, this is just the linkage sanity check + a marker in the
+	 * journal that the binary is wired against the right
+	 * daedalus-fourier version.  Future work (per daedalus-v4l2#11)
+	 * promotes to daedalus_ctx_create() once shader-path resolution
+	 * is wired through the public API.
+	 */
+	daedalus_ctx *df_ctx = daedalus_ctx_create_no_qpu();
+	if (df_ctx) {
+		log_info("daedalus-fourier: linked, ctx alive (no_qpu mode; "
+			 "has_qpu=%d)",
+			 daedalus_ctx_has_qpu(df_ctx));
+	} else {
+		log_warn("daedalus-fourier: ctx_create_no_qpu returned NULL "
+			 "(out of memory?) — continuing without backend kernels");
+	}
+
 	int rc;
 	const char *cmd = argv[i++];
 	if (strcmp(cmd, "parse") == 0) {
@@ -132,6 +154,8 @@ int main(int argc, char **argv)
 		rc = 2;
 	}
 
+	if (df_ctx)
+		daedalus_ctx_destroy(df_ctx);
 	ffmpeg_loader_cleanup(&fm);
 	log_cleanup();
 	return rc;