feat: PDF echeancier + signature DocuSeal + email + page client

EcheancierPdf :
- PDF FPDF avec bloc legal, description, tableau echeances, conditions
- 2 champs signature DocuSeal : Company (auto-signe E-Cosplay) + First Party (client)

Controller :
- generate-pdf : genere le PDF via EcheancierPdf + Vich upload
- send-signature : envoie PDF a DocuSeal (2 parties), email avec bouton signer
- resend : renvoie email proposition
- DocuSealService.getLogoBase64 rendu public

EcheancierProcessController (public) :
- /echeancier/signed/{id} : callback post-signature, passe state a signed

Templates :
- echeancier/signed.html.twig : page confirmation signature client
- emails/echeancier_signature.html.twig : email avec bouton signer
- admin/echeancier/show : boutons generer PDF, voir PDF, envoyer proposition,
  envoyer signature, renvoyer, PDF signe, activer Stripe, annuler

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations/Version20260408174704.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Auto-generated Migration: Please modify to your needs!
+ */
+final class Version20260408174704 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return '';
+    }
+
+    public function up(Schema $schema): void
+    {
+        // this up() migration is auto-generated, please modify it to your needs
+        $this->addSql('ALTER TABLE advert_payment ADD echeancier_id INT DEFAULT NULL');
+        $this->addSql('ALTER TABLE advert_payment ADD CONSTRAINT FK_C766C45B8C858AF2 FOREIGN KEY (echeancier_id) REFERENCES echeancier (id) ON DELETE SET NULL NOT DEFERRABLE');
+        $this->addSql('CREATE INDEX IDX_C766C45B8C858AF2 ON advert_payment (echeancier_id)');
+    }
+
+    public function down(Schema $schema): void
+    {
+        // this down() migration is auto-generated, please modify it to your needs
+        $this->addSql('ALTER TABLE advert_payment DROP CONSTRAINT FK_C766C45B8C858AF2');
+        $this->addSql('DROP INDEX IDX_C766C45B8C858AF2');
+        $this->addSql('ALTER TABLE advert_payment DROP echeancier_id');
+    }
+}