v0.4: licensing — server validation, DPAPI cache, Ed25519 signed responses

UX bonus: clicking "Reprendre" on an interrupted download skips the
release-notes confirmation dialog (the user already approved when they
first clicked Installer).

Server side
-----------
- migrations/001_init.sql: licenses, license_machines, rate_limit,
  audit_log on InnoDB/utf8mb4. Foreign keys, unique on license_key, slot
  uniqueness per (license_id, machine_id).
- api/lib/Db.php: thin PDO singleton (exception mode, prepared, no emul).
- api/lib/Crypto.php: Ed25519 sign/verify via libsodium (sodium_crypto_*),
  HMAC-SHA-256 helper for v0.6, canonicalJson() that strips `signature`
  before serializing — must match exactly the encoding done client-side
  before verify.
- api/routes/ValidateLicense.php: POST /license/validate. Looks up the
  key, walks the machine slot logic (insert or update last_seen),
  enforces max_machines, returns a payload signed Ed25519 + status of
  valid/expired/revoked/machine_limit_exceeded/invalid. Audit logs every
  outcome. Rate-limit 10/min/IP via the rate_limit table.
- tools/generate-keypair.php: prints a fresh sodium keypair so the
  operator drops the hex into config.php and the public_key_hex into the
  launcher resource.
- tools/issue-license.php: PRSRV-XXXX-XXXX-XXXX-XXXX generator (32-char
  unambiguous alphabet), inserts the license, prints the key once.
- tools/sign-manifest.php: now also signs the manifest itself with
  Ed25519 after computing the per-zip sha256s.
- config.example.php: schema rewritten with sections db / hmac / ed25519
  / jwt / rate-limit. config.php remains gitignored.

Client side
-----------
- Models/License.cs: LicenseValidationRequest + LicenseValidationResponse
  with CanDownload(VersionManifest) — entitlement_until vs version's
  minLicenseDate. The status valid|expired|revoked|machine_limit_exceeded
  flow is preserved end-to-end.
- Core/Licensing/LicenseService.cs:
  * machineId = SHA-256 of HKLM/Software/Microsoft/Cryptography/MachineGuid
    + UserName (stable, no PII leak)
  * online ValidateAsync calls /license/validate with launcher version
  * embedded server-pubkey.txt drives Ed25519 verification of the
    response (skipped gracefully if pubkey not yet provisioned)
  * SaveCached / GetCached use DPAPI CurrentUser scope on the license
    key; the cleartext key never touches disk
  * GetCached has a 7-day offline grace window after the last successful
    validation, so going offline doesn't lock the user out
- Core/Resources/server-pubkey.txt: EmbeddedResource. Default content is
  a comment, which the service treats as "no pubkey configured" and
  bypasses verification. Operator pastes the real hex post-deploy and
  rebuilds.
- Core/PSLauncher.Core.csproj: Polly, NSec.Cryptography (Ed25519),
  System.Security.Cryptography.ProtectedData (DPAPI).
- App/Views/OnboardingDialog.xaml(.cs): first-launch / "🔑 Activer"
  modal. Calls LicenseService, displays status messages with red
  foreground on errors and green-tinted secondary text otherwise.
- ViewModels/VersionRowViewModel.cs: new LicenseAllowsDownload property.
  Install button label switches to "🔒 License insuffisante" when the
  user's entitlement_until precedes the version's minLicenseDate;
  CanInstall is false in that case so the click is a no-op too.
- ViewModels/MainViewModel.cs: loads the cached license at startup (no
  network call), surfaces it as LicenseSummary in the top bar, exposes
  ActivateLicenseCommand to (re)open the onboarding dialog. RebuildList
  applies the per-version license filter so older installed versions
  remain launchable but newer-than-license ones can't be downloaded.
- Views/MainWindow.xaml: top bar gains a "🔑 Activer / changer" button
  next to the license summary.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/tools/issue-license.php

@@ -0,0 +1,63 @@
+<?php
+/**
+ * Émet une nouvelle license dans la base. La clé est imprimée en clair sur stdout
+ * (à transmettre au client par canal sécurisé). Aucune trace en clair côté serveur :
+ * la base ne stocke que la clé via UNIQUE pour la lookup constant-time.
+ *
+ * Usage (SSH OVH) :
+ *   php tools/issue-license.php "ACME Corp" 2026-12-31 [maxMachines=1]
+ */
+declare(strict_types=1);
+
+require dirname(__DIR__) . '/api/lib/Db.php';
+$config = require dirname(__DIR__) . '/api/config.php';
+
+if ($argc < 3) {
+    fwrite(STDERR, "Usage: php tools/issue-license.php \"<owner_name>\" <YYYY-MM-DD entitlement_until> [max_machines=1]\n");
+    exit(1);
+}
+
+$owner = $argv[1];
+$until = $argv[2];
+$maxMachines = (int)($argv[3] ?? 1);
+
+if (!preg_match('/^\d{4}-\d{2}-\d{2}$/', $until)) {
+    fwrite(STDERR, "entitlement_until must be YYYY-MM-DD\n"); exit(2);
+}
+
+$db = \PSLauncher\Db::get($config);
+
+// Génère une clé du type PRSRV-XXXX-XXXX-XXXX-XXXX (groupes alphanumériques)
+function genKey(): string {
+    $alphabet = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789'; // pas de 0/O/1/I/L
+    $groups = [];
+    for ($g = 0; $g < 4; $g++) {
+        $s = '';
+        for ($i = 0; $i < 4; $i++) $s .= $alphabet[random_int(0, strlen($alphabet) - 1)];
+        $groups[] = $s;
+    }
+    return 'PRSRV-' . implode('-', $groups);
+}
+
+// Boucle au cas (très improbable) où collision UNIQUE
+for ($attempts = 0; $attempts < 5; $attempts++) {
+    $key = genKey();
+    try {
+        $stmt = $db->prepare(
+            'INSERT INTO licenses (license_key, owner_name, issued_at, download_entitlement_until, max_machines)
+             VALUES (?, ?, NOW(), ?, ?)'
+        );
+        $stmt->execute([$key, $owner, $until . ' 23:59:59', $maxMachines]);
+        $id = $db->lastInsertId();
+        echo "==== License émise ====\n";
+        echo "id     : {$id}\n";
+        echo "owner  : {$owner}\n";
+        echo "until  : {$until}\n";
+        echo "key    : {$key}\n";
+        exit(0);
+    } catch (\PDOException $e) {
+        if (str_contains($e->getMessage(), 'Duplicate')) continue;
+        throw $e;
+    }
+}
+fwrite(STDERR, "Failed to generate unique key after retries\n"); exit(3);