feat(macos): sign and notarize the DMG, app, and server binary

Produce a Gatekeeper-clean macOS distribution with no user workaround:

- Launcher DMG + the LocalAI.app inside it are built via fyne, codesigned
  with the Developer ID under the hardened runtime, then the DMG is signed,
  notarized (notarytool) and stapled. Replaces macos-dmg-creator (which had
  no signing hook) with fyne package + hdiutil so we control the .app before
  packaging.
- The bare local-ai darwin server binary is signed + notarized via
  GoReleaser's native notarize block (quill backend, runs on Linux).
- All signing is gated on secrets being present, so forks/PRs/local builds
  stay unsigned and green (contrib/macos/sign-and-notarize.sh no-ops).
- Add hardened-runtime entitlements and FyneApp.toml for deterministic
  packaging; update macOS install docs to drop the quarantine workaround.

Assisted-by: Claude:claude-opus-4-8 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

contrib/macos/Launcher.entitlements

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <key>com.apple.security.network.client</key>
+    <true/>
+    <key>com.apple.security.network.server</key>
+    <true/>
+    <key>com.apple.security.cs.allow-jit</key>
+    <true/>
+    <key>com.apple.security.cs.allow-unsigned-executable-memory</key>
+    <true/>
+</dict>
+</plist>

contrib/macos/sign-and-notarize.sh

@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+# Code-sign and notarize macOS artifacts for LocalAI.
+# Every sub-command is a no-op (exit 0) when its required secret is unset,
+# so unsigned builds (forks, local dev, PRs) keep working.
+set -euo pipefail
+
+ENTITLEMENTS="contrib/macos/Launcher.entitlements"
+KEYCHAIN="localai-ci.keychain-db"
+
+cmd_import_cert() {
+  if [ -z "${MACOS_CERTIFICATE:-}" ]; then
+    echo "[sign] MACOS_CERTIFICATE unset: skipping cert import (unsigned build)"
+    return 0
+  fi
+  local certfile keychain_pwd default_keychain
+  certfile="$(mktemp).p12"
+  keychain_pwd="${MACOS_CI_KEYCHAIN_PWD:?MACOS_CI_KEYCHAIN_PWD required when signing}"
+  echo "$MACOS_CERTIFICATE" | base64 --decode > "$certfile"
+  security create-keychain -p "$keychain_pwd" "$KEYCHAIN"
+  security set-keychain-settings -lut 21600 "$KEYCHAIN"
+  security unlock-keychain -p "$keychain_pwd" "$KEYCHAIN"
+  security import "$certfile" -k "$KEYCHAIN" -P "${MACOS_CERTIFICATE_PWD:?}" \
+    -T /usr/bin/codesign -T /usr/bin/security
+  security set-key-partition-list -S apple-tool:,apple:,codesign: \
+    -s -k "$keychain_pwd" "$KEYCHAIN" >/dev/null
+  default_keychain="$(security default-keychain | tr -d ' "')"
+  security list-keychains -d user -s "$KEYCHAIN" "$default_keychain"
+  rm -f "$certfile"
+  echo "[sign] certificate imported into $KEYCHAIN"
+}
+
+cmd_sign() {
+  local target="$1"
+  if [ -z "${MACOS_SIGN_IDENTITY:-}" ]; then
+    echo "[sign] MACOS_SIGN_IDENTITY unset: skipping codesign of $target"
+    return 0
+  fi
+  case "$target" in
+    *.app)
+      # Hardened runtime + entitlements are required for notarizing the app bundle.
+      codesign --deep --force --options runtime --timestamp \
+        --entitlements "$ENTITLEMENTS" \
+        --sign "$MACOS_SIGN_IDENTITY" "$target"
+      ;;
+    *)
+      # A disk image carries no entitlements/runtime; just sign the container.
+      codesign --force --timestamp --sign "$MACOS_SIGN_IDENTITY" "$target"
+      ;;
+  esac
+  codesign --verify --strict --verbose=2 "$target"
+  echo "[sign] signed $target"
+}
+
+cmd_notarize() {
+  local dmg="$1"
+  if [ -z "${MACOS_NOTARY_KEY:-}" ]; then
+    echo "[notarize] MACOS_NOTARY_KEY unset: skipping notarization of $dmg"
+    return 0
+  fi
+  local keyfile
+  keyfile="$(mktemp).p8"
+  echo "$MACOS_NOTARY_KEY" | base64 --decode > "$keyfile"
+  xcrun notarytool submit "$dmg" \
+    --key "$keyfile" \
+    --key-id "${MACOS_NOTARY_KEY_ID:?}" \
+    --issuer "${MACOS_NOTARY_ISSUER_ID:?}" \
+    --wait
+  rm -f "$keyfile"
+  xcrun stapler staple "$dmg"
+  xcrun stapler validate "$dmg"
+  echo "[notarize] notarized and stapled $dmg"
+}
+
+main() {
+  local sub="${1:-}"; shift || true
+  case "$sub" in
+    import-cert) cmd_import_cert ;;
+    sign)        cmd_sign "$@" ;;
+    notarize)    cmd_notarize "$@" ;;
+    *) echo "usage: $0 {import-cert|sign <path>|notarize <dmg>}" >&2; exit 2 ;;
+  esac
+}
+
+main "$@"