Add native audio/image efferent surfaces + projector proof-of-shape

audio-surface.el / image-surface.el: own-core additive-synthesis WAV and
raster-PNG renderers (integer-only DSP, since EL has no floats), rendered
from learned engram signatures via a pluggable surface-profile
abstraction (surface-profile.el). audio-demo.el / image-demo.el are
drivers. NOTE: demo files hardcode absolute paths to this worktree's own
directory — will need a path fixup before landing.

elp/projector/ is a Python package the author's own README marks as
"STAGING/PROOF-OF-SHAPE — not the deliverable", superseded by the native
.el surface-profile work above; kept as a validated architecture proof.
Generated output (elp/faculty/{out,sig}, elp/projector/out,
__pycache__) intentionally excluded.

elp/projector/projectors/seams.py

@@ -0,0 +1,60 @@
+"""seams.py — documented efferent seams for IMAGE and VIDEO surfaces.
+
+These are NOT implemented (per the build rails: architect, do not overbuild).
+They are registered as first-class seams so the interface PROVES it accepts
+future non-text projectors without any upstream change. Each documents exactly
+what its decoder would read from the geometry-carrying IR, making the multimodal
+generalization concrete rather than hand-wavy.
+
+The symmetry that guarantees these are possible, not moonshots: they are the
+efferent twins of multimodal INGEST. If meaning can HOLD an image (ingest as
+first-class geometry), meaning can PROJECT one back. Video = image x sound x
+TIME, and the engram already stores time (chronoception). So video falls out of
+an image projector + the music projector + the stored temporal ordering.
+"""
+from __future__ import annotations
+
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+from document_ir import DocumentIR  # noqa: E402
+from projectors.base import register  # noqa: E402
+
+
+class _Seam:
+    """A registered-but-unimplemented projector. Names its decoder contract."""
+
+    def project(self, doc: DocumentIR) -> bytes:  # pragma: no cover - seam
+        raise NotImplementedError(
+            f"{self.surface!r} projector is a documented seam, not yet built. "
+            f"Decoder contract: {self.decoder_contract}")
+
+
+class ImageProjector(_Seam):
+    surface = "image"
+    media_type = "image/png"
+    ext = "png"
+    modality = "image"
+    decoder_contract = (
+        "reads block.provenance as a spatial layout — nodes become regions, edges "
+        "become adjacencies; salience/importance drive size/contrast; polarity "
+        "drives figure/ground. The efferent twin of image ingest (a geometry->raster "
+        "decoder, learned or engineered), exactly mirroring the embedder that turned "
+        "the image INTO geometry.")
+
+
+class VideoProjector(_Seam):
+    surface = "video"
+    media_type = "video/mp4"
+    ext = "mp4"
+    modality = "video"
+    decoder_contract = (
+        "image x sound x TIME. Composes the image projector (per-keyframe geometry "
+        "layout) with the midi/music projector (score) along the geometry's stored "
+        "temporal ordering (chronoception). Needs no new principle once image + music "
+        "exist — only a muxer.")
+
+
+register(ImageProjector())
+register(VideoProjector())