chore(licensing): LGPL FFmpeg swap, third-party notices, attribution hygiene

The MIT OR Apache-2.0 SOURCE license is clean (audit found no copied copyleft); the
gaps were all binary-distribution (Layer-2). This makes the shipped artifacts honest:

- Windows host + client: bundled FFmpeg BtbN gpl-shared -> lgpl-shared (AMF/QSV/decode
  unaffected; the GPL-only x264/x265 were never used), and ship the FFmpeg LGPL notice
  + license text in the installer + MSIX (licenses/).
- THIRD-PARTY-NOTICES.txt generated + bundled into installer/MSIX/deb/rpm. Offline
  generator (scripts/gen-third-party-notices.{py,sh}) + cargo-about config (about.toml/
  .hbs) with a permissive-only accepted-license allow-list as a copyleft regression gate.
- Reword the win32u GPU-preference hook comments to reflect independent reimplementation
  (no Apollo/Sunshine GPL-3.0 source copied).
- README dual-license + inbound=outbound contributor clause + non-affiliation trademark
  disclaimer; new CONTRIBUTING.md.
- LICENSE files into the standalone driver + vk-layer workspaces; deb copyright holder
  aligned to "unom and the punktfunk contributors".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/gen-third-party-notices.py

@@ -0,0 +1,134 @@
+#!/usr/bin/env python3
+"""Generate THIRD-PARTY-NOTICES.txt for the Rust workspace.
+
+Offline, dependency-free attribution generator. It reads `cargo metadata`, then for every
+third-party crate (everything that is NOT a first-party workspace member) it pulls the crate's
+*actual* LICENSE/COPYING/NOTICE text out of the local cargo registry cache (or the in-tree
+vendored source for path deps), deduplicates identical license texts, and emits a single
+notices file: a per-crate manifest followed by the verbatim license texts.
+
+This satisfies the binary-distribution attribution duty for the permissive (MIT/BSD/ISC/Zlib/
+Apache/Unicode/etc.) crates linked into shipped punktfunk artifacts. `cargo about` (see
+about.toml) produces an equivalent, network-augmented result in CI; this is the dependency-free
+fallback that also runs locally and is committed as a baseline.
+
+Usage:  python3 scripts/gen-third-party-notices.py [--out THIRD-PARTY-NOTICES.txt]
+"""
+import argparse
+import hashlib
+import json
+import os
+import subprocess
+import sys
+
+LICENSE_GLOBS = ("license", "licence", "copying", "notice", "unlicense", "copyright")
+
+
+def find_license_files(pkg_dir):
+    out = []
+    try:
+        names = sorted(os.listdir(pkg_dir))
+    except OSError:
+        return out
+    for n in names:
+        low = n.lower()
+        if any(low == g or low.startswith(g + ".") or low.startswith(g + "-") or g in low for g in LICENSE_GLOBS):
+            p = os.path.join(pkg_dir, n)
+            if os.path.isfile(p):
+                try:
+                    with open(p, "r", encoding="utf-8", errors="replace") as f:
+                        txt = f.read().strip()
+                    if txt:
+                        out.append((n, txt))
+                except OSError:
+                    pass
+    return out
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--out", default="THIRD-PARTY-NOTICES.txt")
+    ap.add_argument("--manifest", default="Cargo.toml")
+    args = ap.parse_args()
+
+    meta = json.loads(subprocess.check_output(
+        ["cargo", "metadata", "--format-version", "1", "--offline", "--manifest-path", args.manifest],
+        text=True))
+    ws_members = set(meta.get("workspace_members", []))
+
+    pkgs = []
+    for p in meta["packages"]:
+        if p["id"] in ws_members:
+            continue  # first-party (covered by the root LICENSE-MIT / LICENSE-APACHE)
+        pkgs.append(p)
+    pkgs.sort(key=lambda p: (p["name"].lower(), p["version"]))
+
+    # Group license texts: text-hash -> {text, name, crates[]}
+    texts = {}
+    no_text = []
+    for p in pkgs:
+        pkg_dir = os.path.dirname(p["manifest_path"])
+        files = find_license_files(pkg_dir)
+        label = f'{p["name"]} {p["version"]}'
+        if not files:
+            no_text.append(p)
+            continue
+        for fname, txt in files:
+            h = hashlib.sha256(txt.encode("utf-8", "replace")).hexdigest()
+            ent = texts.setdefault(h, {"text": txt, "filename": fname, "crates": set()})
+            ent["crates"].add(label)
+
+    lines = []
+    w = lines.append
+    w("THIRD-PARTY SOFTWARE NOTICES")
+    w("=" * 76)
+    w("")
+    w("punktfunk (https://git.unom.io/unom/punktfunk) is licensed under MIT OR Apache-2.0.")
+    w("The binaries it ships statically/dynamically link the third-party Rust crates listed")
+    w("below. Each is distributed under its own permissive license; the full license texts")
+    w("follow the manifest. This file is generated by scripts/gen-third-party-notices.py")
+    w("(or `cargo about`, see about.toml) — do not edit by hand.")
+    w("")
+    w(f"Total third-party crates: {len(pkgs)}")
+    w("")
+    w("-" * 76)
+    w("MANIFEST (crate version — SPDX license — source)")
+    w("-" * 76)
+    for p in pkgs:
+        lic = p.get("license") or (("file: " + p["license_file"]) if p.get("license_file") else "UNKNOWN")
+        repo = p.get("repository") or ""
+        w(f'  {p["name"]} {p["version"]} — {lic}' + (f' — {repo}' if repo else ""))
+    w("")
+
+    if no_text:
+        w("-" * 76)
+        w("Crates whose package did not embed a license file (SPDX + source only)")
+        w("-" * 76)
+        for p in no_text:
+            lic = p.get("license") or "UNKNOWN"
+            repo = p.get("repository") or ""
+            w(f'  {p["name"]} {p["version"]} — {lic}' + (f' — {repo}' if repo else ""))
+        w("")
+
+    w("=" * 76)
+    w("FULL LICENSE TEXTS (deduplicated)")
+    w("=" * 76)
+    # Stable order: by first crate name covered.
+    for h, ent in sorted(texts.items(), key=lambda kv: sorted(kv[1]["crates"])[0].lower()):
+        crates = ", ".join(sorted(ent["crates"]))
+        w("")
+        w("-" * 76)
+        w(f"The following license ({ent['filename']}) applies to: {crates}")
+        w("-" * 76)
+        w(ent["text"])
+        w("")
+
+    text = "\n".join(lines) + "\n"
+    with open(args.out, "w", encoding="utf-8") as f:
+        f.write(text)
+    print(f"wrote {args.out}: {len(pkgs)} crates, {len(texts)} distinct license texts, "
+          f"{len(no_text)} without embedded text", file=sys.stderr)
+
+
+if __name__ == "__main__":
+    main()