feat(knowledge): add retry endpoint and 20-char text name limit

Add POST /api/tenant/knowledge/items/retry/:id to re-queue failed parse
tasks, plus a 20-rune cap on text item names with matching frontend
validation. Wires the retry button into the knowledge table with a
colored status tag for clearer state feedback.

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

server/internal/tenant/transport/router.go

@@ -199,6 +199,7 @@ func RegisterRoutes(app *bootstrap.App) {
 	knowledge.POST("/items/text", knowledgeHandler.CreateTextItem)
 	knowledge.POST("/items/url", knowledgeHandler.CreateURLItem)
 	knowledge.POST("/items/file", knowledgeHandler.CreateFileItem)
+	knowledge.POST("/items/retry/:id", knowledgeHandler.RetryItem)
 	knowledge.DELETE("/items/:id", knowledgeHandler.DeleteItem)
 
 	// Prompt Rules