feat: two-way sync between support tickets and Gitea issues (v0.63.0)

Outbound (already existed one-way: ticket create -> Gitea issue) now
also mirrors status changes: closing/reopening a ticket in the admin
UI closes/reopens the linked Gitea issue, and replies posted from
Epicure (by the ticket owner or an admin) post as a comment on the
issue. Captures and stores the Gitea issue number at creation time
to address these follow-up calls without re-parsing the issue URL.

Inbound: new webhook receiver at /api/webhooks/gitea, verified via
HMAC-SHA256 signature (X-Gitea-Signature) with a configurable
GITEA_WEBHOOK_SECRET site setting, deduped by delivery id the same
way the existing Stripe receiver dedupes events. Handles "issues"
(closed/reopened -> ticket status) and "issue_comment" (created ->
appends to the ticket's comment thread), skipping comments Epicura
already posted itself (matched by Gitea comment id) to avoid loops.

New support_ticket_comments table backs a lightweight conversation
thread on both the user-facing support page and the admin support
manager, each comment tagged by author (user/admin/gitea).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/messages/fr.json

@@ -492,6 +492,16 @@
     "historyTitle": "Vos tickets",
     "noTickets": "Vous n'avez encore rien soumis.",
     "viewIssue": "Voir le ticket",
+    "conversation": "Conversation",
+    "noComments": "Aucune réponse pour l'instant.",
+    "commentPlaceholder": "Écrire une réponse…",
+    "commentSend": "Envoyer",
+    "commentSendFailed": "Échec de l'envoi de la réponse",
+    "commentAuthor": {
+      "user": "Vous",
+      "admin": "Équipe Epicure",
+      "gitea": "Équipe Epicure"
+    },
     "status": {
       "open": "Ouvert",
       "triaged": "Trié",